Polymer aerogel with improved mechanical and thermal properties

ABSTRACT

An aerogel that includes an open-cell structured polymer matrix is disclosed. The aerogel includes 5 wt. % to 50 wt. % of a polyamic amide polymer, based on the total weight of the aerogel, pores and at least 90% of the pore volume of the aerogel is made up of macropores, a porosity of at least 50%, as measure according to ASTM D4404-10, a density of 0.01 g/cm 3  to 0.5 g/cm 3 , and the aerogel is thermally stable to resist browning at 330° C.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. application Ser. No.16/820,351 filed Mar. 16, 2020, which is a continuation of U.S.application Ser. No. 15/963,839 filed Apr. 26, 2018 (now U.S. Pat. No.10,626,239), which is a divisional of U.S. application Ser. No.15/616,458 filed Jun. 7, 2017 (now U.S. Pat. No. 9,963,571), whichclaims priority to U.S. Provisional Application No. 62/347,424 filedJun. 8, 2016. The contents of the referenced applications areincorporated into the present application by reference.

BACKGROUND OF THE INVENTION A. Field of the Invention

The present disclosure relates to the field of aerogels. In particular,the invention concerns aerogels having a polymeric matrix that includesa polyamic amide polymer.

B. Description of Related Art

A gel by definition is a spongelike, three-dimensional solid networkwhose pores are filled with another non-gaseous substance, such as aliquid. The liquid of the gel is not able to diffuse freely from the gelstructure and remains in the pores of the gel. Drying of the gel thatexhibits unhindered shrinkage and internal pore collapse during dryingprovides materials commonly referred to as xerogels.

By comparison, a gel that dries and exhibits little or no shrinkage andinternal pore collapse during drying can yield an aerogel. An aerogel isa light weight material having a relatively low density and highporosity (about 94-99%). Aerogels are used in a wide variety ofapplications such as building and construction, aerospace, catalysts,insulation, sensors, thickening agents, and the like. Aerogels made fromorganic polymers (e.g., polyimides or silica/polyimide blends) providelightweight, low-density structures; however, they tend to have lowerglass transition temperatures and degrade at higher temperatures (>150°C.). Attempts to improve the thermal properties of polymer aerogels haveincluded cross-linking tri, tetra, or poly-functional units in thestructure. Although cross-linked polymer aerogels (e.g., polyimideaerogels) can have some acceptable mechanical properties, they typicallysuffer from poor flexibility and can be difficult to manufacture,reprocess, or recycle. The lack of manufacturability and recyclabilitycan have a negative impact on production scale-up, large scalemanufacturing, conformation to irregular surfaces, or maintainingintegrity in dynamic conditions.

Recent efforts to improve upon the flexibility of aerogels, while stillmaintaining good thermal and mechanical properties, have been focused onmodifying the polymers used to create the aerogel matrix. For example,U.S. Pat. No. 9,109,088 to Meader et al., discloses cross-linkedpolyimide aerogels that attempt to impart bulk flexibility by usingflexible linking groups in the polymer backbone. U.S. Pat. No. 9,206,298to Rodman et al., suggests that specific properties of polyimidepolymers, such as flexibility, can be influenced by incorporatingcertain compounds into the polyimide polymer without the formulation ofcovalent bonds. However, the resultant properties of the non-covalentlylinked compounds can be difficult to predict. For instance,non-covalently linked compounds in the polymer matrix can aggregate,which can affect homogeneity, mechanical properties, and otherproperties of the final aerogel.

Despite the foregoing, the above mentioned aerogels can still sufferfrom brittleness, poor thermal stability, and/or complicatedmanufacturing steps.

SUMMARY OF THE INVENTION

A discovery has been made that provides a solution to at least some ofthe aforementioned problems associated with polyimide aerogels. Thediscovery is premised on an aerogel containing a polyamic amide polymerwithin its polymer matrix. The aerogels of the present invention canhave high branching and little to no crosslinking. It was surprisinglyfound that the polyamic amide aerogel of the present invention exhibitshigher flexibility, higher thermal stability, and lower thermalconductivity than existing polyimide-based aerogels. The disclosedaerogels are stable and are able to resist browning at 330° C. Inaddition, the presence of polyamic amide in the polymer matrices of theaerogels of the present invention are easier to manufacture and/orrecycle. By way of example, the methods of producing the polyamic amideaerogels of the present invention can eliminate or reduce the need forcostly reagents and complex manufacturing steps, which are difficult tocontrol.

Still further, and in certain non-limiting aspects, the polymericmatrices of the aerogels of the present invention can include macropores(pores having a size of greater than 50 nanometers (nm) in diameter),mesopores (pores having a size of 2 nm to 50 nm in diameter), ormicropores (pores having a size of less than 2 nm in diameter), or anycombination of such pores (e.g., macropores and mesopores, macroporesand micropores, macropores, mesopores, and micropores, or mesopores andmicropores). In certain preferred embodiments, the aerogels of thepresent invention include macropores. It is believed that the presenceof macropores can further help facilitate the manufacturing of theaerogels, as macropores are larger and less likely to collapse duringthe drying stage of manufacturing when compared with micropores and/ormesopores. This can result in a more economically efficient and lesscomplicated drying process, thereby allowing for a more commerciallyscalable process when compared with known mesoporous and/or microporousstructured aerogels. Additionally, the presence of macropores mayimprove any one of or all of the flexibility, strength, gas permeation,and/or the strength to density ratio of the formed aerogel. In morepreferred instances, the average pore size of the porous aerogelmatrices of the present invention is greater than 50 nm to 5000 nm indiameter, preferably 100 nm to 2000 nm in diameter, more preferably 500nm to 2000 nm in diameter, even more preferably 1000 nm to 1400 nm indiameter, still more preferably 1100 nm to 1300 nm in diameter, and mostpreferably about 1200 nm in diameter. Additionally, and in somepreferred embodiments, the majority (e.g., more than 50%) of the porevolume in the aerogels of the present invention can be made up frommacropores. In even further instances, over 55%, 60%, 70%, 80%, 90%,95%, 99%, or 100% of the pore volume of the aerogels can be made up ofmacropores. In instances where less than 100% of the pore volume is madeup of macropores, such aerogels can also include mesopores and/ormicropores. This porous architecture along with the incorporation of theaforementioned polyamic amide polymers into the aerogels is believed tocontribute to the improved mechanical, thermal, manufacturability,and/or recyclability properties of the aerogels of the presentinvention.

In one embodiment of the present invention there is disclosed an aerogelincluding a polyamic amide polymer. The aerogel can include an open-cellstructured polymer matrix that includes the polyamic amide polymer. Thepolyamic amide polymer can have a repeating structural unit of:

where X can be a first organic group having at least two carbon atoms, Ycan be a second organic group having at least two carbon atoms, and Zcan be a nitrogen containing hydrocarbon compound that includes at leastone secondary nitrogen. In some instances, the above polyamic amidepolymer can be 2 to 2000 repeating units in length. In one aspect, Z canbe a substituted or an unsubstituted cyclic compound, a substituted oran unsubstituted aromatic compound, or combinations thereof. In anotheraspect, Z can further include at least one tertiary nitrogen. By way ofexample, Z can be an imidazole or a substituted imidazole, a triazole ora substituted triazole, a tetrazole or substituted tetrazole, a purineor a substituted purine, a pyrazole or a substituted pyrazole, orcombinations thereof, and, in some instances, the secondary and tertiarynitrogen atoms are separated by at least one carbon atom. In a oneaspect, Z has the following general structure:

where R₃, R₄, and R₅ can each individually be a hydrogen (H) atom, analkyl group, or a substituted alkyl group, an aromatic group or asubstituted aromatic group, or R₄, and R₅ come together with other atomsto form a fused ring structure. In some instances, the aforementionedalkyl group or substituted alkyl group can have 1 to 12 carbon atoms, 2to 6 carbon atoms, 3 to 8 carbon atoms, 5 to 12 carbon atoms, preferably1 to 6 carbon atoms. In other instances, R₃ can be a methyl group or anethyl group, and R₄ and R₅ can be H atoms, an alkyl group, or asubstituted alkyl group. In some aspects, R₃ can be a methyl group, andR₄ and R₅ are H atoms. R₃ can be an ethyl group, and R₄ and R₅ are eachindividually a H, an alkyl group, or a substituted alkyl, preferably, R₄is a methyl group and R₅ is a H atom. In some instances, the aerogel ofthe present invention can include at least 5 wt. % of the polyamic amidepolymer based on the total weight of the polymer aerogel. In oneparticular instance, the aerogel of the present invention can include 5wt. % to 50 wt. % of the polyamic amide polymer based on the totalweight of the polymer aerogel. In another instance, the aerogel of thepresent invention can include 5 wt. % to 25 wt. % of the polyamic amidepolymer based on the total weight of the polymer aerogel. The aerogel ofthe present invention can include 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15,16, 17, 18, 19, 20, 21, 22, 23, 24, 25, 26, 27, 28, 29, 30, 31, 32, 33,34, 35, 36, 37, 38, 39, 40, 41, 42, 43, 44, 45, 46, 47, 48, 49, or 50wt. % of the polyamic amide polymer based on the total weight of thepolymer aerogel. In another aspect, the aerogels of the presentinvention can have any one, any combination of, or all of the followingcharacteristics: (1) a density of 0.05 g/cm³ to 0.35 g/cm³; (2) aporosity of at least 50, 60, 70, 80, or 90%, preferably at least 85%,and more preferably 85% to 95%; and/or (3) a tensile strength of 100 psito 2500 psi (0.69 MPa to 17.23 MPa) and an elongation of 0.1% to 50%, atroom temperature as measured according to ASTM D882-02. (4) acompression strength of 10 psi to 500 psi (0.069 MPa to 3.45 MPa) at 10%strain at room temperature as measured according to ASTM D395-14, (5) orcombinations thereof.

In another embodiment of the present invention, the polyamic amideaerogel further includes a repeating structural unit of:

where Y can be hydroquinone dianhydride;3,3′,4,4′-biphenyltetracarboxylic dianhydride; pyromellitic dianhydride;3,3′,4,4′-benzophenone-tetracarboxylic dianhydride; anhydride;3,3′,4,4′-diphenylsulfone-tetracarboxylic dianhydride;4,4′-(4,4′-isopropylidenediphenoxy)bis(phthalic anhydride);bis(3,4-dicarboxyphenyl)propane dianhydride;4,4′-(hexafluoroisopropylidene)diphthalic anhydride;bis(3,4-dicarboxyphenyl)sulfoxide dianhydride; polysiloxane-containingdianhydride; 2,2′,3,3′-biphenyltetracarboxylic dianhydride;2,3,2′,3′-benzophenonetetracarboxylic dianhydride;3,3′,4,4′-benzophenonetetracarboxylic dianhydride;naphthalene-2,3,6,7-tetracarboxylic dianhydride;naphthalene-1,4,5,8-tetracarboxylic dianhydride; 4,4′-oxydiphthalicdianhydride; 3,3′,4,4′-biphenylsulfone tetracarboxylic dianhydride;3,4,9,10-perylene tetracarboxylic dianhydride;bis(3,4-dicarboxyphenyl)sulfide dianhydride;bis(3,4-dicarboxyphenyl)methane dianhydride;2,2-bis(3,4-dicarboxyphenyl)propane dianhydride;2,2-bis(3,4-dicarboxyphenyl)hexafluoropropene;2,6-dichloronaphthalene-1,4,5,8-tetracarboxylic dianhydride;2,7-dichloronapthalene-1,4,5,8-tetracarboxylic dianhydride;2,3,6,7-tetrachloronaphthalene-1,4,5,8-tetracarboxylic dianhydride;phenanthrene-8,9,10-tetracarboxylic dianhydride;pyrazine-2,3,5,6-tetracarboxylic dianhydride;benzene-1,2,3,4-tetracarboxylic dianhydride;thiophene-2,3,4,5-tetracarboxylic dianhydride; or combinations thereof.In some instances, the above polyimide polymer can be 2 to 2000repeating units in length. In one aspect, the aerogel can include acopolymer including two repeating structural units of:

where m and n are an average number of repeat units per chain rangingfrom 1 to 2000. In another aspect, the copolymer can be a branchedcopolymer and the aerogel includes an open-cell structure.

In other embodiments, there is also disclosed a polymer having a generalrepeating structural unit of:

where X can be first organic group having at least two carbon atoms, Ycan be a second organic group having at least two carbon atoms, and Zcan be nitrogen containing hydrocarbon compound including at least onesecondary nitrogen. In some aspects, the polymer can be included in acopolymer where the co-polymer includes repeating units of:

where m and n are the average number of repeat units per chain rangingfrom 1 to 2000. In another aspect, the polymer can be further includedin an aerogel. In some aspects, any of the aforementioned polymers canhave a branched polymer matrix. In some embodiments, the matrix containsless than 5% by weight of crosslinked polymers. The branched polymermatrix of the aerogel composition can include less than 1% by weight ofcrosslinked polymers. In some embodiments, the branched polymer matrixof the aerogel composition is not crosslinked. In some embodiments, theaerogel composition includes a hyperbranched polymer. A hyperbranchedpolymer is a highly branched macromolecule with three-dimensionaldendritic architecture. The branched and hyperbranched polymers caninclude multifunctional amines and the like. In some embodiments, thebranched polyimides can include a degree of branching (DB) of at least0.2, 0.3, 0.4, 0.5, or more branches per polyimide polymer chain. Infurther embodiments, DB may range from 0.2 to 10. In some instances, theDB can be 0.2 to 1 or any value or range therein (e.g., 0.2. 0.3, 0.4,0.5, 0.6, 0.7, 0.8, 0.9, or 1). In one preferred instance, the DB can be0.2 to 0.7, 0.2 to 0.4, 0.3 to 0.4, or preferably about 0.32. In anotherinstance, the DB can be 0.4 to 0.7, 0.4 to 0.6, 0.45 to 0.55, orpreferably about 0.51. In another aspect, the DB can range from 1.2 to8, or from 3 to 7. In a particular embodiment, the degree of branchingis about 6.3.

Also disclosed is a method of making aerogels of the present invention.The method can include (a) providing at least one diamine compound to asolvent to form a solution; (b) providing at least one dianhydridecompound to the solution of step (a) under conditions sufficient to forma polyamic acid solution; (c) providing a secondary amine to thepolyamic acid solution; (d) subjecting the mixture of step (c) toconditions suitable to produce a polymer matrix solution including apolyamic amide; and (e) subjecting the polymer matrix solution toconditions sufficient to form an aerogel. The secondary amine of themethod can be a substituted or an unsubstituted cyclic amine, asubstituted or an unsubstituted aromatic amine, or combinations thereof.In some aspects, the secondary amine can include at least one secondarynitrogen and at least one tertiary nitrogen (e.g., an imidazole or asubstituted imidazole, a triazole or a substituted triazole, a tetrazoleor substituted tetrazole, a purine or a substituted purine, a pyrazoleor a substituted pyrazole, or combinations thereof). In some instances,the nitrogen atoms are separated by at least one carbon atom. In certainaspects, the secondary amine in step (c) has the following generalstructure:

where R₃, R₄, and R₅ are defined above. In further aspects, step (d) ofthe method includes providing a dehydrating agent prior to, during, orafter adding the secondary amine. Subjecting the polymer matrix solutionto conditions sufficient to form an open-cell structure can include theaddition of sufficient amounts of chemical curing agents for sufficientamounts of time to form a gel. The method can further include subjectingthe gel to a drying step to remove the solvent and the drying step canbe subcritical drying, supercritical drying or evaporative air drying,or any combination thereof. Even further, the method can include (i)subjecting the gel to conditions sufficient to freeze the solvent toform a frozen material, and (ii) subjecting the frozen material to asubcritical drying step sufficient to form an open-cell structure. Incertain aspects, subjecting the polymer matrix solution to conditionssufficient to form an open-cell structure can include removing thesolvent under a stream of air or subjecting the polymer matrix solutionto at least one solvent exchange with a different solvent (e.g.,acetone). In other aspects, the method can also include amultifunctional amine.

In instances where there is a desire to incorporate macropores into thepolymeric matrix of any one of the aerogels of the present invention,such macropores can be formed by selecting processing conditions thatfavor the formation of macropores vs mesopores and/or micropores. Theamount of macropores can be adjusted by implementing any one of, anycombination of, or all of the following variables: (1) thepolymerization solvent; (2) the polymerization temperature; (3) thepolymer molecular weight; (4) the molecular weight distribution; (5) thecopolymer composition; (6) the amount of branching; (7) the amount ofcrosslinking; (8) the method of branching; (9) the method ofcrosslinking; (10) the method used in formation of the gel; (11) thetype of catalyst used to form the gel; (12) the chemical composition ofthe catalyst used to form the gel; (13) the amount of the catalyst usedto form the gel; (14) the temperature of gel formation; (15) the type ofgas flowing over the material during gel formation; (16) the rate of gasflowing over the material during gel formation; (17) the pressure of theatmosphere during gel formation; (18) the removal of dissolved gassesduring gel formation; (19) the presence of solid additives in the resinduring gel formation; (20) the amount of time of the gel formationprocess; (21) the substrate used for gel formation; (22) the type ofsolvent or solvents used in each step of the solvent exchange process;(23) the composition of solvent or solvents used in each step of thesolvent exchange process; (24) the amount of time used in each step ofthe solvent exchange process; (25) the dwell time of the part in eachstep of the solvent exchange process; (26) the rate of flow of thesolvent exchange solvent; (27) the type of flow of the solvent exchangesolvent; (28) the agitation rate of the solvent exchange solvent; (29)the temperature used in each step of the solvent exchange process; (30)the ratio of the volume of solvent exchange solvent to the volume of thepart; (31) the method of drying; (32) the temperature of each step inthe drying process; (33) the pressure in each step of the dryingprocess; and/or (34) the solvents used in each step of the dryingprocess. In one preferred and non-limiting aspect, the formation ofmacropores vs smaller mesopores and micropores can be primarilycontrolled by controlling the polymer/solvent dynamics during gelformation. By doing so, the pore structure can be controlled, and thequantity and volume of macroporous, mesoporous, microporous cells can becontrolled. In one instance, this can be done by adding a curing agentto the solution to reduce the solubility of polymers formed in thesolution and to form macropores in the gel matrix, the formed macroporescontaining liquid from the solution. For example, a curing additive thatreduces the resultant polymer solubility, such as1,4-diazabicyclo[2.2.2]octane, can produce a polymer matrix containing ahigher number of macropores compared to another curing additive thatimproves the resultant polyimide solubility, such as triethylamine. Inanother example, using the same dianhydride such asbiphenyl-tetracarboxylic acid dianhydride (BPDA), but increasing theratio of rigid amines incorporated into the polymer backbone such asp-phenylenediamine (p-PDA) as compared to more flexible diamines such as4,4′-oxydianiline (ODA), the formation of macropores as compared tosmaller mesopores and micropores can be controlled.

The aerogel of the present invention can be included in articles ofmanufacture. Articles of manufacture can be a thin film, a monolith, awafer, a blanket, a core composite material, a substrate forradiofrequency antenna, a substrate for a sunshield, a substrate for asunshade, a substrate for radome, insulating material for oil and/or gaspipeline, insulating material for liquefied natural gas pipeline,insulating material for cryogenic fluid transfer pipeline, insulatingmaterial for apparel, insulating material for aerospace applications,insulating material for buildings, cars, and other human habitats,insulating material for automotive applications, insulation forradiators, insulation for ducting and ventilation, insulation for airconditioning, insulation for heating and refrigeration and mobile airconditioning units, insulation for coolers, insulation for packaging,insulation for consumer goods, vibration dampening, wire and cableinsulation, insulation for medical devices, support for catalysts,support for drugs, pharmaceuticals, and/or drug delivery systems,aqueous filtration apparatus, oil-based filtration apparatus, andsolvent-based filtration apparatus, or any combination thereof.Preferably, the article of manufacture is an antenna, a sunshield orsunscreen, a radome, a blanket, or a filter.

The aerogel of the present invention can be used to filter a fluid inneed thereof. A filtration method using the aerogel of the presentinvention can include contacting a feed fluid with the aerogel of thepresent invention under conditions sufficient to remove at least aportion of the impurities and/or desired substances from the feed fluidand produce a filtrate. In one aspect, the feed fluid is a liquid, agas, a supercritical fluid, or a mixture thereof. The feed fluid caninclude water or alternatively can be a non-aqueous liquid. When thefeed fluid is a non-aqueous liquid, it can be an oil, a solvent, orcombinations thereof. In a specific aspect, the feed fluid is a solventand the solvent can be an organic solvent. In another specific aspect,the feed fluid is an emulsion and the emulsion can be a water-oilemulsion, an oil-water emulsion, a water-solvent emulsion, asolvent-water emulsion, an oil-solvent emulsion, or a solvent-oilemulsion. The feed fluid can also be a biological fluid and thebiological fluid can be blood, plasma, or both. Additionally, the feedfluid can be a gas and the gas can include air, nitrogen, oxygen, aninert gas, or mixtures thereof. The goal of the method of filtering afluid using the disclosed aerogels is to obtain a filtrate that issubstantially free of impurities and/or a desired substance. In anotherembodiment, a filtration system is disclosed that includes (a) anaerogel of the present invention, and (b) a separation zone in fluidcommunication with the aerogel, a feed fluid and a filtrate.

Also disclosed in the context of the present invention are embodiments 1to 64. Embodiment 1 is an aerogel comprising an open-cell structuredpolymer matrix that includes a polyamic amide polymer. Embodiment 2 isthe aerogel of embodiment 1, wherein the polyamic amide polymer in thematrix has a repeating structural unit of:

where X is a first organic group having at least two carbon atoms, Y isa second organic group having at least two carbon atoms, and Z is anitrogen containing hydrocarbon compound comprising at least onesecondary nitrogen. Embodiment 3 is the aerogel of claim 2, wherein Z isa substituted or an unsubstituted cyclic compound, a substituted or anunsubstituted aromatic compound, or combinations thereof. Embodiment 4is the aerogel of any one of embodiments 2 to 3, wherein Z furthercomprises at least one tertiary nitrogen. Embodiment 5 is the aerogel ofembodiment 4, wherein Z is an imidazole or a substituted imidazole, atriazole or a substituted triazole, a tetrazole or substitutedtetrazole, a purine or a substituted purine, a pyrazole or a substitutedpyrazole, or combinations thereof. Embodiment 6 is the aerogel ofembodiment 4, wherein the secondary and tertiary nitrogen atoms areseparated by at least one carbon atom. Embodiment 7 is the aerogel ofembodiment 6, wherein Z has the following general structure:

where R₃, R₄, and R₅ are each individually a hydrogen (H) atom, an alkylgroup, or a substituted alkyl group, an aromatic group or a substitutedaromatic group, or R₄, and R₅ come together with other atoms to form afused ring structure. Embodiment 8 is the aerogel of embodiment 7,wherein the alkyl group or a substituted alkyl group has 1 to 12 carbonatoms, 2 to 6 carbon atoms, 3 to 8 carbon atoms, 5 to 12 carbon atoms,preferably 1 to 6 carbon atoms. Embodiment 9 is the aerogel of any oneof embodiments 7 to 8, wherein R₃ is a methyl group or an ethyl groupand R₄ and R₅ are H atoms, an alkyl group, or a substituted alkyl group.Embodiment 10 is the aerogel of embodiment 9, wherein R₃ is a methylgroup, and R₄ and R₅ are H atoms. Embodiment 11 is the aerogel ofembodiment 9, wherein R₃ is an ethyl group and R₄ and R₅ are eachindividually a H atom, an alkyl group, or a substituted alkyl,preferably, R₄ is a methyl group and R₅ is a H atom. Embodiment 12 isthe aerogel of any one of embodiments 1 to 11, further comprising apolyimide polymer. Embodiment 13 is the aerogel of embodiment 12,wherein the polyimide polymer has a repeating structural unit of:

Embodiment 14 is the aerogel of any one of embodiments 1 to 13, whereinthe Y is derived from hydroquinone dianhydride;3,3′,4,4′-biphenyltetracarboxylic dianhydride; pyromellitic dianhydride;3,3′,4,4′-benzophenone-tetracarboxylic dianhydride; 4,4′-oxydiphthalicanhydride; 3,3′,4,4′-diphenylsulfone-tetracarboxylic dianhydride;4,4′-(4,4′-isopropylidenediphenoxy)bis(phthalic anhydride);2,2-bis(3,4-dicarboxyphenyl)propane dianhydride;4,4′-(hexafluoroisopropylidene)diphthalic anhydride;bis(3,4-dicarboxyphenyl)sulfoxide dianhydride; polysiloxane-containingdianhydride; 2,2′,3,3′-biphenyltetracarboxylic dianhydride;2,3,2′,3′-benzophenonetetraearboxylic dianhydride;3,3′,4,4′-benzophenonetetraearboxylic dianhydride;naphthalene-2,3,6,7-tetracarboxylic dianhydride;naphthalene-1,4,5,8-tetracarboxylic dianhydride; 4,4′-oxydiphthalicdianhydride; 3,3′,4,4′-biphenylsulfone tetracarboxylic dianhydride;3,4,9,10-perylene tetracarboxylic dianhydride;bis(3,4-dicarboxyphenyl)sulfide dianhydride;bis(3,4-dicarboxyphenyl)methane dianhydride;2,2-bis(3,4-dicarboxyphenyl)propane dianhydride;2,2-bis(3,4-dicarboxyphenyl)hexafluoropropene;2,6-dichloronaphthalene-1,4,5,8-tetracarboxylic dianhydride;2,7-dichloronapthalene-1,4,5,8-tetracarboxylic dianhydride;2,3,6,7-tetrachloronaphthalene-1,4,5,8-tetracarboxylic dianhydride;phenanthrene-8,9,10-tetracarboxylic dianhydride;pyrazine-2,3,5,6-tetracarboxylic dianhydride;benzene-1,2,3,4-tetracarboxylic dianhydride;thiophene-2,3,4,5-tetracarboxylic dianhydride; or combinations thereof.Embodiment 15 is the aerogel of any one of embodiments 1 to 14, whereinthe aerogel is a copolymer comprising two repeating structural units of:

where m and n are average number of repeat units per chain ranging from1 to 2000. Embodiment 16 is the aerogel of embodiment 15, wherein thecopolymer is a branched copolymer. Embodiment 17 is the aerogel of anyone of embodiments 1 to 16, wherein the polymer matrix comprises atleast 5 wt. %, preferably 5 wt. % to 50 wt. %, or more preferably 5 wt.% to 25 wt. %, of the polyamic amide polymer. Embodiment 18 is theaerogel of any one of embodiments 1 to 16, wherein the polymer matrixhas an average pore size of greater than 50 nanometers (nm) to 5000 nmin diameter, preferably 100 nm to 2000 nm in diameter, more preferably500 nm to 2000 nm in diameter, even more preferably 1000 nm to 1400 nmin diameter, still more preferably 1100 nm to 1300 nm in diameter, andmost preferably about 1200 nm in diameter. Embodiment 19 is the aerogelof embodiment 18, wherein the polymer matrix has an average pore size of1000 nm to 1400 nm in diameter. Embodiment 20 is the aerogel ofembodiment 19, wherein the polymer matrix has an average pore size of1100 nm to 1300 nm, preferably about 1200 nm in diameter.

Embodiment 21 is a polymer having a general repeating structural unitof:

where X is first organic group having at least two carbon atoms, Y issecond organic group having at least two carbon atoms, Z is nitrogencontaining hydrocarbon compound comprising at least one secondarynitrogen. Embodiment 22 is the polymer of embodiment 21, wherein thepolymer is comprised in a copolymer. Embodiment 23 is the polymer ofembodiment 22, wherein the co-polymer comprises repeating units of:

where m and n are average number of repeat units per chain ranging from1 to 2000. Embodiment 24 is the polymer of any one of embodiments 21 to23, further comprised in an aerogel of any one of claims 1 to 23.

Embodiment 25 is a method of making the aerogel of any one ofembodiments 1 to 20, the method comprising: (a) providing at least onediamine compound to a solvent to form a solution; (b) providing at leastone dianhydride compound to the solution of step (a) under conditionssufficient to form a polyamic acid solution; (c) providing a secondaryamine to the polyamic acid solution; (d) subjecting the solution of step(c) to conditions suitable to produce a polymer matrix solutioncomprising a polyamic amide; and (e) subjecting the polymer matrixsolution to conditions sufficient to form an aerogel comprising anopen-cell structured polymer matrix that includes the polyamic amide.Embodiment 26 is the method of embodiment 25, wherein the secondaryamine is a substituted or an unsubstituted cyclic amine, a substitutedor an unsubstituted aromatic amine, or combinations thereof. Embodiment27 is the method of any one of embodiments 25 to 26, wherein secondaryamine further comprises at least one secondary nitrogen and at least onetertiary nitrogen. Embodiment 28 is the method of embodiment 27, whereinthe secondary amine is imidazole or a substituted imidazole, a triazoleor a substituted triazole, a tetrazole or substituted tetrazole, apurine or a substituted purine, a pyrazole or a substituted pyrazole, orcombinations thereof. Embodiment 29 is the method of embodiment 28,wherein the nitrogen atoms are separated by at least one carbon atom.Embodiment 30 is the method of any one of embodiments 25 to 29, whereinthe secondary amine in step (c) has the following general structure:

where R₃, R₄, and R₅ are each individually a hydrogen, an alkyl group,or a substituted alkyl group, or an aromatic group or a substitutedgroup, or R₄, and R₅ come together with other atoms to form a cyclicstructure. Embodiment 31 is the method of embodiment 30, wherein thealkyl group has 1 to 12 carbon atoms, 2 to 6 carbon atoms, 3 to 8 carbonatoms, 5 to 12 carbon atoms, preferably 1 to 6 carbon atoms. Embodiment32 is the method of any one of embodiments 30 to 31, wherein R₃ is amethyl group or an ethyl group, and R₄ and R₅ are H atoms, an alkylgroup, or a substituted alkyl. Embodiment 33 is the method of embodiment32, wherein R₃ is a methyl group and R₄ and R₅ are H atoms. Embodiment34 is the method of embodiment 32, wherein R₃ is an ethyl group and R₄and R₅ are each individually a H atom, an alkyl group, or a substitutedalkyl, preferably, R₄ is a methyl group and R₅ is a H atom. Embodiment35 is the method of any one of embodiments 25 to 34, wherein step (d)comprises providing a dehydrating agent prior to, during, or after,adding the secondary amine. Embodiment 36 is the method of any one ofembodiments 25 to 35, wherein subjecting the polymer matrix solution toconditions sufficient to form an aerogel comprises the addition ofsufficient amounts of chemical curing agents for sufficient amounts oftime to form a gel. Embodiment 37 is the method of embodiment 36,further comprising subjecting the gel to a drying step to remove thesolvent. Embodiment 38 is the method of embodiment 37, wherein thedrying step is subcritical drying or supercritical drying. Embodiment 39is the method of embodiment 38, further comprising: (i) subjecting thegel to conditions sufficient to freeze the solvent to form a frozenmaterial; and (ii) subjecting the frozen material to a subcriticaldrying step sufficient to form an open-cell structure. Embodiment 40 isthe method of embodiment 37, wherein the drying step is evaporativedrying. Embodiment 41 is the method of any one of embodiments 25 to 40,wherein subjecting the polymer matrix solution to conditions sufficientto form an open-cell structure comprises removing the solvent under astream of air. Embodiment 42 is the method of embodiment 41, furthercomprising subjecting the polymer matrix solution to at least onesolvent exchange with a different solvent. Embodiment 43 is the methodof embodiment 42, wherein at least one solvent exchange is performedwith acetone.

Embodiment 44 is an article of manufacture comprising the aerogel of anyone of embodiments 1 to 20 or the polymer of any one of embodiments 21to 24. Embodiment 45 is the article of manufacture of embodiment 44,wherein the article of manufacture is a thin film, monolith, wafer,blanket, core composite material, a substrate for radiofrequencyantenna, substrate for a sunshield, a substrate for a sunshade, asubstrate for radome, insulating material for oil and/or gas pipeline,insulating material for liquefied natural gas pipeline, insulatingmaterial for cryogenic fluid transfer pipeline, insulating material forapparel, insulating material for aerospace applications, insulatingmaterial for buildings, cars, and other human habitats, insulatingmaterial for automotive applications, insulation for radiators,insulation for ducting and ventilation, insulation for air conditioning,insulation for heating and refrigeration and mobile air conditioningunits, insulation for coolers, insulation for packaging, insulation forconsumer goods, vibration dampening, wire and cable insulation,insulation for medical devices, support for catalysts, support fordrugs, pharmaceuticals, and/or drug delivery systems, aqueous filtrationapparatus, oil-based filtration apparatus, and solvent-based filtrationapparatus, or any combination thereof. Embodiment 46 is the article ofmanufacture of embodiment 45, wherein the article of manufacture is anantenna. Embodiment 47 is the article of manufacture of embodiment 45,wherein the article of manufacture is a sunshield or sunscreen.Embodiment 48 is the article of manufacture of embodiment 45, whereinthe article of manufacture is a radome. Embodiment 49 is the article ofmanufacture of embodiment 45, wherein the article of manufacture is afilter.

Embodiment 50 is a method of filtering a fluid comprising impuritiesand/or desired substances, the method comprising contacting a feed fluidwith the aerogel of any one of embodiments 1 to 20 under conditionssufficient to remove at least a portion of the impurities and/or desiredsubstances from the feed fluid and produce a filtrate. Embodiment 51 isthe method of embodiment 50, wherein the feed fluid is a liquid, a gas,a supercritical fluid, or a mixture thereof. Embodiment 52 is the methodof embodiment 51, wherein the feed fluid comprises water. Embodiment 53is the method of embodiment 52, wherein the feed fluid is a non-aqueousliquid. Embodiment 54 is the method of embodiment 53, wherein thenon-aqueous liquid is an oil, a solvent, or combinations thereof.Embodiment 55 is the method of embodiment 54, wherein the feed fluid isa solvent. Embodiment 56 is the method of embodiment 55, wherein thesolvent is an organic solvent. Embodiment 57 is the method of any one ofembodiments 50 to 56, wherein the feed fluid is an emulsion. Embodiment58 is the method of embodiment 57, wherein the emulsion is a water-oilemulsion, an oil-water emulsion, a water-solvent emulsion, asolvent-water emulsion, an oil-solvent emulsion, or a solvent-oilemulsion. Embodiment 59 is the method of embodiment 50, wherein the feedfluid is a biological fluid. Embodiment 60 is the method of embodiment59, wherein the biological fluid is blood, plasma, or both. Embodiment61 is the method of embodiment 50, wherein the feed fluid is a gas.Embodiment 62 is the method of embodiment 61, wherein the gas comprisesair, nitrogen, oxygen, an inert gas, or mixtures thereof. Embodiment 63is the method of any one of embodiments 50 to 62, wherein the filtrateis substantially free of impurities and/or a desired substance.

Embodiment 64 is a filtration system comprising: (a) the aerogel of anyone of embodiments 1 to 20; and (b) a separation zone in fluidcommunication with the aerogel, a feed fluid and a filtrate.

The following includes definitions of various terms and phrases usedthroughout this specification.

The term “aerogel” refers to a class of materials that are generallyproduced by forming a gel, removing a mobile interstitial solvent phasefrom the pores, and then replacing it with a gas or gas-like material.By controlling the gel and evaporation system, density, shrinkage, andpore collapse can be minimized. As explained above, aerogels of thepresent invention can include micropores, mesopores, or macropores, orany combination thereof. The amount of micropores, mesopores, and/ormacropores in any given aerogel of the present invention can be modifiedor tuned as desired. In certain preferred aspects, however, the aerogelscan include macropores such that at least 5%, 10%, 15%, 20%, 25%, 30%,35%, 40%, 45%, 50%, 55%, 60%, 65%, 70%, 75%, 80%, 85%, 90%, 95%, or 100%of the aerogel's pore volume can be made up of macropores. In someembodiments, the aerogels of the present invention can have low bulkdensities (about 0.25 g/cm³ or less, preferably about 0.01 to 0.5g/cm³), high surface areas (generally from about 10 to 1,000 m²/g andhigher, preferably about 50 to 1000 m²/g), high porosity (about 80% andgreater, preferably greater than about 85%), and/or relatively largepore volume (more than about 1.0 mL/g, preferably about 1.2 mL/g andhigher).

The presence of macropores, mesopores, and/or micropores in the aerogelsof the present invention can be determined by mercury intrusionporosimetry (MIP) and/or gas physisorption experiments. In a preferredinstance, the MIP test used in the Examples section can be used (i.e.,American Standard Testing Method (ASTM) D4404-10, Standard Test Methodfor Determination of Pore Volume and Pore Volume Distribution of Soiland Rock by Mercury Intrusion Porosimetry).

The terms “impurity” or “impurities” refers to unwanted substances in afeed fluid that are different than a desired filtrate and/or areundesirable in a filtrate. In some instances, impurities can be solid,liquid, gas, or supercritical fluid. In some embodiments, an aerogel canremove some or all of an impurity.

The term “desired substance” or “desired substances” refers to wantedsubstances in a feed fluid that are different than the desired filtrate.In some instances, the desired substance can be solid, liquid, gas, orsupercritical fluid. In some embodiments, an aerogel can remove some orall of a desired substance.

The term “radio frequency (RF)” refers to the region of theelectromagnetic spectrum having wavelengths ranging from 10⁻⁴ to 10⁷ m.

The term “supercritical fluid” refers to any substance at a temperatureand pressure above its critical point. A supercritical fluid can diffusethrough solids like a gas, and dissolve materials like a liquid.Additionally, close to the critical point, small changes in pressure ortemperature result in large changes in density.

The use of the words “a” or “an” when used in conjunction with any ofthe terms “comprising,” “including,” “containing,” or “having” in theclaims, or the specification, may mean “one,” but it is also consistentwith the meaning of “one or more,” “at least one,” and “one or more thanone.”

The terms “about” or “approximately” are defined as being close to asunderstood by one of ordinary skill in the art. In one non-limitingembodiment, the terms are defined to be within 10%, preferably within5%, more preferably within 1%, and most preferably within 0.5%.

The term “substantially” and its variations are defined to includeranges within 10%, within 5%, within 1%, or within 0.5%.

The use of the term “or” in the claims is used to mean “and/or” unlessexplicitly indicated to refer to alternatives only or the alternativesare mutually exclusive, although the disclosure supports a definitionthat refers to only alternatives and “and/or.”

As used in this specification and claim(s), the words “comprising” (andany form of comprising, such as “comprise” and “comprises”), “having”(and any form of having, such as “have” and “has”), “including” (and anyform of including, such as “includes” and “include”) or “containing”(and any form of containing, such as “contains” and “contain”) areinclusive or open-ended and do not exclude additional, unrecitedelements or method steps.

The polyamic amide aerogel of the present invention can “comprise,”“consist essentially of,” or “consist of” particular ingredients,components, compositions, etc. disclosed throughout the specification.With respect to the transitional phase “consisting essentially of,” inone non-limiting aspect, a basic and novel characteristic of thepolyamic amide aerogel of the present invention is that it has improvedmechanical and/or thermal properties due to the presence of a polyamicamide polymer in the aerogel matrix.

Other objects, features and advantages of the present invention willbecome apparent from the following figures, detailed description, andexamples. It should be understood, however, that the figures, detaileddescription, and examples, while indicating specific embodiments of theinvention, are given by way of illustration only and are not meant to belimiting. Additionally, it is contemplated that changes andmodifications within the spirit and scope of the invention will becomeapparent to those skilled in the art from this detailed description. Infurther embodiments, features from specific embodiments may be combinedwith features from other embodiments. For example, features from oneembodiment may be combined with features from any of the otherembodiments. In further embodiments, additional features may be added tothe specific embodiments described herein.

BRIEF DESCRIPTION OF THE DRAWINGS

Advantages of the present invention may become apparent to those skilledin the art with the benefit of the following detailed description andupon reference to the accompanying drawings.

FIG. 1 is a reaction schematic showing the synthesis of a polyimidepolymer including polyisoimide.

FIG. 2 is a reaction schematic of an embodiment showing the synthesis ofa polyimide polymer including polyamic amide.

FIG. 3 is a schematic of system of an embodiment for filtering a fluidusing a polyamic amide aerogel, the system having a separation zone, aninlet, and an outlet.

FIG. 4 is a schematic of system of an embodiment for filtering a fluidusing a polyamic amide aerogel, the system having a separation zone andan inlet.

FIG. 5 is a schematic of system of an embodiment for filtering a fluidusing a polyamic amide aerogel, the system having a separation zone andan outlet.

FIG. 6 distribution of pore diameters of an aerogel monolith of thepresent invention obtained by freeze drying.

FIG. 7 distribution of pore diameters of an aerogel monolith of thepresent invention obtained by freeze drying.

FIG. 8 distribution of pore diameters of an aerogel monolith of thepresent invention obtained by freeze drying.

While the invention is susceptible to various modifications andalternative forms, specific embodiments thereof are shown by way ofexample in the drawings and may herein be described in detail. Thedrawings may not be to scale.

DETAILED DESCRIPTION OF THE INVENTION

A discovery has been made that provides a polyamic amide containingaerogel with improved mechanical and thermal properties as well asimproved manufacturability and processability over conventionalpolyimide aerogels. These and other non-limiting aspects of the presentinvention are discussed in further detail in the following sections.

A. Polyamic Amide Polymer

In a particular embodiment, the aerogel of the current inventionincludes a polymeric matrix having a polyamic amide polymer. Thepresence of the polyamic amide polymer surprisingly provides the aerogelwith many improved properties over conventional polyimide aerogels. Insome embodiments, the polymer aerogels contain little to no polyisoimidebyproduct in the polymer matrix. In general, polyamic amide polymersinclude two amides that are part of the polymer backbone, and at leasttwo additional amides that are not part of the polymer backbone. The atleast two amides not part of the polymer backbone are free to rotate andinteract with functional groups within and not within the polymerbackbone. This structural arrangement may help to reduce the linearityand stiffness of the polymer backbone in a way to benefit theflexibility of the resultant aerogel while retaining or even increasingmechanical and thermal properties. The amides not part of the polymerbackbone can also be variably functionalized with different amines toprovide further opportunity for chemical interactions and theinstallation of further functionality to further affect aerogelproperties. Similar to polyimide polymer, polyamic amide polymer can beconsidered an AA-BB type polymer because usually two different classesof monomers are used to produce the polyamic amide polymer. Howeverpolyamic amides are different than polyimides in that the intermediatepolyamic acid derivative can be reacted with a free amine instead ofcyclodehydration to form the polyimide. Polyamic amides can also beprepared from AB type monomers. For example, an aminodicarboxylic acidmonomer can be polymerized to form an AB type intermediate polyamic acidthat can be treated with a free amine under condition to form a polyamicamide. Monoamines and/or mono anhydrides can be used as end cappingagents if desired.

The polyamic amide of the current invention has a repeating structuralunit of:

where X can be a first organic group having at least two carbon atoms, Ycan be a second organic group having at least two carbon atoms, and Zcan be a nitrogen containing hydrocarbon compound comprising at leastone secondary nitrogen. Z can be a substituted or an unsubstitutedcyclic compound, a substituted or an unsubstituted aromatic compound, orcombinations thereof. In some instances, the above polyamic amidepolymer can be 2 to 2000 repeating units in length. Z can also includeat least one tertiary nitrogen, and, in some instances, the secondaryand tertiary nitrogen atoms are separated by at least one carbon atom.Non-limiting examples of Z compounds include an imidazole or asubstituted imidazole, a triazole or a substituted triazole, a tetrazoleor substituted tetrazole, a purine or a substituted purine, a pyrazoleor a substituted pyrazole, or combinations thereof. More specifically, Zcan have the following general structure:

where R₃, R₄, and R₅ can be each individually a hydrogen (H) atom, analkyl group, or a substituted alkyl group, an aromatic group or asubstituted aromatic group, or R₄, and R₅ come together with other atomsto form a fused ring structure. In some instances, the imidazole canundergo electrophilic aromatic acylation to bond a carbon atom of theimidazole with the carbonyl carbon bonded to Y. An alkyl group can be astraight or branched chain alkyl having 1 to 20 carbon atoms andincludes, for example, methyl, ethyl, propyl, isopropyl, butyl,isobutyl, secondary butyl, tertiary butyl, pentyl, isopentyl, neopentyl,hexyl, heptyl, octyl, 2-ethylhexyl, 1,1,3,3-tetramethylbutyl, nonyl,decyl, dodecyl, tetradecyl, hexadecyl, octadecyl, and eicosyl. Asubstituted alkyl group can be any of the aforementioned alkyl groupsthat are additionally substituted with an heteroatom, such as a halogen(F, Cl, Br, I), boron, oxygen, nitrogen, sulfur, silicon, etc. Anaromatic group can be any aromatic hydrocarbon group having from 6 to 20carbon atoms of the monocyclic, polycyclic or condensed polycyclic type,and include, for example, phenyl, biphenyl and naphthyl. A substitutedaromatic group can be any of the aforementioned aromatic groups that areadditionally substituted with an heteroatom, such as a halogen (F, Cl,Br, I), boron, oxygen, nitrogen, sulfur, silicon, etc. A fused ringstructure includes, for example, benzimidazole. In some instances, theaforementioned alkyl group or substituted alkyl group has 1 to 12 carbonatoms, 2 to 6 carbon atoms, 3 to 8 carbon atoms, 5 to 12 carbon atoms,preferably 1 to 6 carbon atoms. In other instances, R₃ can be a methylgroup or an ethyl group and R₄ and R₅ are H atoms, an alkyl group, or asubstituted alkyl group. In some aspects, R₃ can be a methyl group, andR₄ and R₅ are H atoms, and, in other aspects, R₃ can be an ethyl groupand R₄ and R₅ are each individually a H, an alkyl group, or asubstituted alkyl, preferably, R₄ is a methyl group and R₅ is a H atom.The polyamic amide can have the following general structure when Z is animidazole or substituted imidazole:

In a particular embodiment, the polyamic amide polymer is:

The polyamic amide polymer can be synthesized by several methods. In onemethod of synthesizing the aromatic polyamic amide polymer, a solutionof the aromatic diamine in a polar aprotic solvent, such asN-methylpyrrolidone (NMP), is prepared. A di-acid monomer, usually inthe form of a dianhydride, is added to this solution, but the order ofaddition of the monomers can be varied. For example, the di-acid monomercan be added first, or the di-acid monomer and the diamine can besimultaneously added. The resulting polycondensation reaction forms apolyamic acid, also referred to as a polyamide acid, which is a polyamicamide precursor. Other polyamic amide precursors are known, includingpolyamic ester, polyamic acid salts, polysilyl esters, andpolyisoimides. Once the polyamic acid or derivative is formed, it can befurther reacted with a nitrogen containing hydrocarbon and dehydrationagent under conditions to form the polyamic amide polymer. The nitrogencontaining hydrocarbon and dehydration agent together or separately maybe present in solution, added during the reaction process, or added in aseparate step as appropriate so the nitrogen containing hydrocarbon canbe incorporated into the polyamic amide polymer by an amidation process.“Amidation” is defined as the conversion of a polyamic amide precursorinto an polyamic amide. In some aspects, the molar ratio of a nitrogencontain hydrocarbon to anhydride or diamine monomer can be from 0.031:1to 128:1, 0.12:1 to 32:1, or specifically from 0.5:1 to 8:1. The molarratio of nitrogen containing hydrocarbon to dehydration agent can befrom 01:1 to 44:1, 0.04:1 to 11:1, or specifically from 0.17:1 to 2.8:1.In general, amidation reactions, such as the reaction between acarboxylic acid and amine to form a amide bond are thermodynamicallyfavorable, but often suffer from a high activation energy due acid-basechemistry between the carboxylic acid and amine. To overcome the highactivation energy, amidation reactions often rely on non-acidicactivation of the acid derivative. Activation can be achieved using adehydration agent. For example, the activated acid derivative can bemixed with an acetic anhydride such as trifluoroacetic anhydride (TFAA)and trifluoroacetic acid (TFA) in toluene. In a preferred embodiment,amidation to form polyamic amide polymer can be achieved using anorganic compound having a at least one secondary amine. In oneparticular instance, an organic compound having a secondary and atertiary amine, such as 2-methyl imidazole or 2-ethyl-4-methylimidazolecan be used. The dehydration agent can include acetic anhydride,propionic anhydride, n-butyric anhydride, benzoic anhydride,trifluoroacetic anhydride, oxalyl chloride, thionyl chloride, phosphorustrichloride, dicyclohexylcarbodiimide, 1,1′-carbonyldiimidazole (CDI),di-tert-butyl dicarbonate (Boc₂O), or combinations thereof.

B. Polyimide Polymer

In another embodiment, the polymeric matrices of the aerogels of thepresent invention can also include a polyimide polymer. Polyimidespolymers can be used in production of aerogels with many desirableproperties. In general, polyimide polymers include a nitrogen atom inthe polymer backbone, where the nitrogen atom is connected to twocarbonyl carbons, such that the nitrogen atom is somewhat stabilized bythe adjacent carbonyl groups. A carbonyl group includes a carbon,referred to as a carbonyl carbon, which is double bonded to an oxygenatom. Polyimides are usually considered an AA-BB type polymer becauseusually two different classes of monomers are used to produce thepolyimide polymer. Polyimides can also be prepared from AB typemonomers. For example, an aminodicarboxylic acid monomer can bepolymerized to form an AB type polyimide. Monoamines and/or monoanhydrides can be used as end capping agents if desired.

The polyimide of the current invention has a repeating structural unitof:

where X can be a first organic group having at least two carbon atomsand Y can be a second organic group having at least two carbon atoms,where X and Y are defined above. In some instances, the above polyimidepolymer can be 2 to 2000 repeating units in length.

Polyimides may be synthesized by several methods. In one method ofsynthesizing aromatic polyimides, a solution of the aromatic diamine ina polar aprotic solvent, such as N-methylpyrrolidone (NMP), is prepared.A di-acid monomer, usually in the form of a dianhydride, is added tothis solution, but the order of addition of the monomers can be varied.For example, the di-acid monomer can be added first, or the di-acidmonomer and the diamine can be simultaneously added. The resultingpolycondensation reaction forms a polyamic acid, also referred to as apolyamide acid, which is a polyimide precursor. Other polyimideprecursors are known, including polyamic ester, polyamic acid salts,polysilyl esters, and polyisoimides. This process description may beapplicable to one or more polyimide precursor solutions. Alternativelythe polyimide can be formed from the forward or reverse mixing of aminesand anhydrides under appropriate dehydrating conditions and/or catalystswhere the lifetime of the polyamic acid intermediate is very short orpossibly not even detectable. The polyimide polymer is formed by acyclodehydration reaction, also called imidization. “Imidization” isdefined as the conversion of a polyimide precursor into an imide.Alternatively, polyamic acids or other precursors may be converted insolution to polyimides by using a chemical dehydrating agent, catalyst,and/or heat.

C. Highly Branched Non-Crosslinked Aerogel

In some aspects, the present disclosure provides an aerogel thatincludes an open-cell structure and a branched polymer matrix. In someembodiments, the matrix contains less than 5%, less than 4%, less than3%, or less than 2% by weight of crosslinked polymers. The branchedpolymer matrix of the aerogel composition can include less than 1% byweight of crosslinked polymers. In some embodiments, the branchedpolymer matrix of the aerogel composition is not crosslinked.

The characteristics or properties of the final aerogel can be impactedby the choice of monomers used to produce the aerogel. Factors to beconsidered when selecting monomers include the properties of the finalaerogel, such as the flexibility, thermal stability, coefficient ofthermal expansion (CTE), coefficient of hydroscopic expansion (CHE) andany other properties specifically desired, as well as cost. Often,certain important properties of a polymer for a particular use can beidentified. Other properties of the polymer may be less significant, ormay have a wide range of acceptable values; so many different monomercombinations could be used. The aerogel composition of the currentinvention includes a high degree of branching and low degree ofcrosslinking, which has a positive effect the polymers' mechanicalproperties. A highly crosslinked polymer is typically considered athermoset polymer, which is a polymer that has been irreversibly cured.The polymers presented herein display a low degree of crosslinking,thereby more closely resembling a thermoplastic. As such, the polymermay be re-shaped and re-cycled. In some aspects, the current aerogelcomposition includes polyamic amide polymer containing a large amount oftrifunctional, tetrafunctional, or multifunctional monomer, specificallytriamine monomer, yet displays little to no crosslinking.

Other factors to be considered in the selection of monomers include theexpense and availability of the monomers chosen. Commercially availablemonomers that are produced in large quantities generally decrease thecost of producing polymer materials since such monomers are in generalless expensive than monomers produced on a lab scale and pilot scale.Additionally, the use of commercially available monomers can improve theoverall reaction efficiency because additional reactions are notrequired to produce a monomer, which is then incorporated into thepolymer.

The highly branched aerogels of the current invention may contain imideco-monomer units that include relatively rigid molecular structures suchas aromatic/cyclic moieties. These typical structures may often berelatively linear and stiff. The linearity and stiffness of thecyclic/aromatic backbone reduces segmental rotation and allows formolecular ordering which results in lower coefficient of thermalexpansion than many thermoplastic polymers having more flexible chains.In addition, the intermolecular associations of polyimide chains provideresistance to most solvents, which tends to reduce the solubility ofmany typical polyimide polymers in many solvents. In some aspects, theuse of more aliphatic monomers can reduce the stiffness of the aerogel,if desired.

In some embodiments, the aerogel composition can include a hyperbranchedpolymer. A hyperbranched polymer is a highly branched macromolecule withthree-dimensional dendritic architecture. Hence, the molecular weight ofa hyperbranched polymer is not a sufficient parameter that characterizesthese polymers. Since the number of possible structures becomes verylarge as the polymerization degree of macromolecules increases, there isa need to characterize also this aspect of hyperbranched polymers. Thus,the term degree of branching (DB) was introduced as a quantitativemeasure of the branching perfectness for hyperbranched polymers. In someembodiments, the branched polyimides of the current aerogels can includea degree of branching (DB) of at least 0.2, 0.3, 0.4, 0.5, or morebranches per polyimide polymer chain. In further embodiments, DB mayrange from 0.2 to 10, preferably from 1.2 to 8, or more preferably from3 to 7. In a particular embodiment, the degree of branching is 6.3.Alternatively, the DB may range from 0.2 to 5, preferably 0.2 to 1, morepreferably 0.2 to 0.6, or even more preferably about 0.2 to 0.4, orabout 0.32. In another aspect, the DB may range from 0.3 to 0.7, 0.4 to0.6, or about 0.51. In some aspects, DB may be represented by thefollowing equation:

$\frac{2Q_{T}}{3 - Q_{T} + {3Q_{M}} - {3p}}$

where p is the extent of reaction, and Q_(T) and Q_(M) are parametersrepresenting the fractions of monofunctional and trifunctional monomersat the beginning of the reaction according to the following equations:

$\begin{matrix}{Q_{T} = \frac{3N_{T}}{N_{M} + {2N_{B}} + {3N_{T}}}} \\{Q_{M} = \frac{N_{M}}{N_{M} + {2N_{B}} + {3N_{T}}}}\end{matrix}$

where N_(T), N_(M), and N_(B) are the initial number of trifunctional,monofunctional, and bifunctional monomers, respectively.

The highly branched non-crosslinked aerogels of the current inventioncan be prepared from step-growth polymers. Step-growth polymers are agroup of polymeric chemicals that have many uses and beneficialproperties. Step-growth polymers can be formed via step-growthpolymerization in which bifunctional or multifunctional monomers reactto form first dimers, then trimers, then longer oligomers and eventuallylong chain polymers. Generally, step-growth polymers can have robustmechanical properties including toughness and high temperatureresistance that make them desirable over other polymer types. There arenumerous varieties of step-growth polymers, including, polyamic amides,polyimides, polyurethanes, polyureas, polyamides, phenolic resins,polycarbonates, and polyesters. In one embodiment the aerogels of thecurrent invention include a polyamic amide polymer. In anotherembodiment the aerogels of the current invention include a polyamicamide polymer and a polyimide polymer.

The characteristics or properties of the final polymer are significantlyimpacted by the choice of monomers, which are used to produce thepolymer. Factors to be considered when selecting monomers include theproperties of the final polymer, such as the flexibility, thermalstability, coefficient of thermal expansion (CTE), coefficient ofhydroscopic expansion (CHE) and any other properties specificallydesired, as well as cost. Often, certain important properties of apolymer for a particular use can be identified. Other properties of thepolymer may be less significant, or may have a wide range of acceptablevalues; so many different monomer combinations could be used.

D. Aerogel Polymer Compositions

In certain embodiments the aerogel of the current invention includes apolymer or copolymer having repeating units of polyamic amide andpolyimide:

where m and n are the average number of repeat units per chain rangingfrom 1 to 2000. In one aspect the average number of m can be 1 to 2000,preferably 10 to 1000, and the average number of n can be 1 to 2000,preferably 10 to 1000. In another aspect the ratio of m:n can be 0.001:1to 1000:1, preferably 0.1:1 to 10:1. The polymers and copolymers can beproduced by first preparing a polyamic acid intermediate in situ. Thepolyamic acid intermediate can then be transformed into a of polyamicamide polymer, a polyimide polymer, or a mixture thereof. In oneembodiment, the polyamic acid can be further reacted with a nitrogencontaining hydrocarbon to form a polyamic amide polymer. In anotherembodiment, polyamic acid can be formed into a sheet or a film andsubsequently processed with heat (often temperatures higher than 250°C.) or both heat and catalysts to convert the polyamic acid to apolyimide. This process can also be applied after the polyamic acid hasbeen treated with a nitrogen containing hydrocarbon to prepare a mixedpolymer containing both polyamic amide monomer and polyimide monomer orcopolymer. A copolymer can also be prepared by controlling the amount ofamidation versus imidization. One method to control the ratio of m:nincludes limiting or providing in excess the nitrogen containinghydrocarbon, such as a secondary amine in the reaction available foramidation. Without being limited to theory, it is believed thatcontrolling the amount, or type of, dehydration agent, temperature,solvent, and/or reaction time can also contribute to the ratio of m:n.Another benefit of an aerogel polymer composition containing polyamicamide polymers is that during the formation of the polyamic amide littleto no polyisoimide is formed.

In some instances, the polyamic acid intermediate can be moisturesensitive, and care must be taken to avoid the uptake of water into thepolymer solution. Additionally, some polyamic acid intermediates exhibitself-imidization in solution as they gradually convert to the polyimidestructure. The imidization reaction can reduce the polymer solubilityand produce water as a by-product. The produced water can then reactwith the remaining polyamic acid, thereby cleaving the polymer chain,thus polyamic acids are used, in some instances, in situ, or directlyafter isolation.

In some aspects, the precursors or intermediates that are formed to makethe aerogel polymer composition, including polyamic acid, polyamic acidsalt precursors, or polyamic amide precursors can be soluble in thereaction solvent. In this instance, the soluble precursor solutions canbe cast into a film on a suitable substrate such as by spin casting,gravure coating, three roll coating, knife over roll coating, slot dieextrusion, dip coating, Meyer rod coating, or other techniques. The castfilm can then be heated in stages to elevated temperatures to removesolvent and convert, for example, the amic acid functional groups in theprecursor to polyamic amide through amidation with an appropriatenitrogen containing hydrocarbon, to polyimide by imidization, or byapplying appropriate conditions to afford a mixed copolymer.

One class of monomer used to prepare the polymers and copolymers of thecurrent invention can be a diamine, or a diamine monomer. The diaminemonomer can also be a diisocyanate, and it is to be understood that anisocyanate could be substituted for an amine in this description, asappropriate. The other type of monomer can be an acid monomer, (e.g., adianhydride) or a di-acid monomer. Di-acid monomers can include adianhydride, a tetraester, a diester acid, a tetracarboxylic acid, or atrimethylsilyl ester, all of which can react with a diamine to produce apolyamic acid intermediate that can be used to prepare a polyamic amidepolymer or copolymer. Dianhydrides are sometimes referred to in thisdescription, but it is to be understood that tetraesters, diester acids,tetracarboxylic acids, or trimethylsilyl esters could be substituted, asappropriate.

Because one di-acid monomer has two anhydride groups, different diaminomonomers can react with each anhydride group so the di-acid monomer canbecome located between two different diamino monomers. The diaminemonomer contains two amine functional groups; therefore, after the firstamine functional group attaches to one di-acid monomer, the second aminefunctional group is still available to attach to another di-acidmonomer, which then attaches to another diamine monomer, and so on. Inthis manner, the polymer backbone is formed. The resultingpolycondensation reaction forms a polyamic acid.

The aerogel polymer compositions containing polyamic amide polymer areusually formed from two different types of monomers, and it is possibleto mix different varieties of each type of monomer. Therefore, one, two,or more di-acid monomers can be included in the reaction vessel, as wellas one, two or more diamino monomers. The total molar quantity ofdi-acid monomers is kept about the same as the total molar quantity ofdiamino monomers if a long polymer chain is desired. Because more thanone type of diamine or di-acid can be used, the various monomerconstituents of each polymer chain can be varied to produce aerogelpolymer compositions with different properties. For example, a singlediamine monomer AA can be reacted with two di-acid co monomers, B₁B₁ andB₂B₂, to form a polymer chain of the general form(AA-B₁B₁)_(x)-(AA-B₂B₂)_(y) in which x and y are determined by therelative incorporations of B₁B₁ and B₂B₂ into the polymer backbone.Alternatively, diamine co-monomers A₁A₁ and A₂A₂ can be reacted with asingle di-acid monomer BB to form a polymer chain of the general form of(A₁A₁-BB)_(x)-(A₂A₂-BB)_(y). Additionally, two diamine co-monomers A₁A₁and A₂A₂ can be reacted with two di-acid co-monomers B₁B₁ and B₂B₂ toform a polymer chain of the general form(A₁A₁-B₁B₁)_(w)-(A₁A₁-B₂B₂)_(x)-(A₂A₂-B₁B₁)_(y)-(A₂A₂-B₂B₂)_(z), wherew, x, y, and z are determined by the relative incorporation ofA₁A₁-B₁B₁, A₁A₁-B₂B₂, A₂A₂-B₁B₁, and A₂A₂-B₂B₂ into the polymerbackbone. More than two di-acid co-monomers and/or more than two diamineco-monomers can also be used. Therefore, one or more diamine monomerscan be polymerized with one or more di-acids, and the general form ofthe polymer is determined by varying the amount and types of monomersused.

There are many examples of monomers that can be used to make the aerogelpolymer compositions containing polyamic amide polymer of the presentinvention. In some embodiments, the diamine monomer is a substituted orunsubstituted aromatic diamine, a substituted or unsubstitutedalkyldiamine, or a diamine that can include both aromatic and alkylfunctional groups. A non-limiting list of possible diamine monomersinclude 4,4′-oxydianiline, 3,4′-oxydianiline, 3,3′-oxydianiline,p-phenylenediamine, m-phenylenediamine, o-phenylenediamine,diaminobenzanilide, 3,5-diaminobenzoic acid,3,3′-diaminodiphenylsulfone, 4,4′-diaminodiphenyl sulfones,1,3-bis-(4-aminophenoxy)benzene, 1,3-bis-(3-aminophenoxy)benzene,1,4-bis-(4-aminophenoxy)benzene, 1,4-bis-(3-aminophenoxy)benzene,2,2-Bis[4-(4-aminophenoxy)phenyl]-hexafluoropropane,2,2-bis(3-aminophenyl)-1,1,1,3,3,3-hexafluoropropane,4,4′-isopropylidenedianiline,1-(4-aminophenoxy)-3-(3-aminophenoxy)benzene,1-(4-aminophenoxy)-4-(3-aminophenoxy)benzene,bis-[4-(4-aminophenoxy)phenyl]sulfones,2,2-bis[4-(3-aminophenoxy)phenyl]sulfones,bis(4-[4-aminophenoxy]phenyl)ether,2,2′-bis-(4-aminophenyl)-hexafluoropropane, (6F-diamine),2,2′-bis-(4-phenoxyaniline)isopropylidene, meta-phenylenediamine,para-phenylenediamine, 1,2-diaminobenzene, 4,4′-diaminodiphenylmethane,2,2-bis(4-aminophenyl)propane, 4,4′diaminodiphenylpropane,4,4′-diaminodiphenyl sulfide, 4,4′-diaminodiphenyl sulfone,3,4′-diaminodiphenylether, 4,4′-diaminodiphenylether,2,6-diaminopyridine, bis(3-aminophenyl)diethyl silane,4,4′-diaminodiphenyl diethyl silane, benzidine, dichlorobenzidine,3,3′-dimethoxybenzidine, 4,4′-diaminobenzophenone,N,N-bis(4-aminophenyl)-n-butylamine, N,N-bis(4-aminophenyl)methylamine,1,5-diaminonaphthalene, 3,3′-dimethyl-4,4′-diaminobiphenyl,4-aminophenyl-3-aminobenzoate, N,N-bis(4-aminophenyl)aniline,bis(p-beta-amino-t-butylphenyl)ether,p-bis-2-(2-methyl-4-aminopentyl)benzene,p-bis(1,1-dimethyl-5-aminopentyl)benzene,1,3-bis(4-aminophenoxy)benzene, m-xylenediamine, p-xylenediamine,4,4′-diaminodiphenyletherphosphine oxide, 4,4′-diaminodiphenylN-methylamine, 4,4′-diaminodiphenyl N-phenylamine, amino-terminalpolydimethylsiloxanes, amino-terminal polypropyleneoxides,amino-terminal polybutyleneoxides,4,4′-methylenebis(2-methylcyclohexylamine), 1,2-diaminoethane,1,3-diaminopropane, 1,4-diaminobutane, 1,5-diaminopentane,1,6-diaminohexane, 1,7-diaminoheptane, 1,8-diaminooctane,1,9-diaminononane, 1,10-diaminodecane, 4,4′-methylenebisbenzeneamine,2,2′-dimethylbenzidine, (also known as4,4′-diamino-2,2′-dimethylbiphenyl (DMB), bisaniline-p-xylidene,4,4′-bis(4-aminophenoxy)biphenyl, 3,3′-bis(4 aminophenoxy)biphenyl,4,4′-(1,4-phenylenediisopropylidene)bisaniline, and4,4′-(1,3-phenylenediisopropylidene)bisaniline, or combinations thereof.In a specified embodiment, the diamine monomer is 4,4′-oxydianiline,2,2′-dimethylbenzidine, or both.

A non-limiting list of possible dianhydride monomers includehydroquinone dianhydride, 3,3,4,4′-biphenyltetracarboxylic dianhydride(BPDA), pyromellitic dianhydride, 3,3′,4,4′-benzophenonetetracarboxylicdianhydride, 4,4′-oxydiphthalic anhydride,3,3′,4,4′-diphenylsulfonetetracarboxylic dianhydride, 4,4′-(4,4isopropylidenediphenoxy)bis(phthalic anhydride),2,2-bis(3,4-dicarboxyphenyl)propane dianhydride,4,4′-(hexafluoroisopropylidene)diphthalic anhydride,bis(3,4-dicarboxyphenyl) sulfoxide dianhydride, polysiloxane-containingdianhydride, 2,2′,3,3′-biphenyltetracarboxylic dianhydride,2,3,2′,3′-benzophenonetetraearboxylic dianhydride,3,3′,4,4′-benzophenonetetraearboxylic dianhydride,naphthalene-2,3,6,7-tetracarboxylic dianhydride,naphthalene-1,4,5,8-tetracarboxylie dianhydride, 4,4′-oxydiphthalicdianhydride, 3,3′,4,4′-biphenylsulfonetetracarboxylic dianhydride,3,4,9,10-perylene tetracarboxylic dianhydride,bis(3,4-dicarboxyphenyl)sulfide dianhydride,bis(3,4-dicarboxyphenyl)methane dianhydride,2,2-bis(3,4-dicarboxyphenyl)propane dianhydride,2,2-bis(3,4-dicarboxyphenyl)hexafluoropropane,2,6-dichloronaphthalene-1,4,5,8-tetracarboxylic dianhydride,2,7-dichloronapthalene-1,4,5,8-tetracarboxylic dianhydride,2,3,6,7-tetrachloronaphthalene-1,4,5,8-tetracarboxylic dianhydride,phenanthrene-, 8,9,10-tetracarboxylic dianhydride,pyrazine-2,3,5,6-tetracarboxylic dianhydride,benzene-1,2,3,4-tetracarboxylic dianhydride, andthiophene-2,3,4,5-tetracarboxylic dianhydride, or combinations thereof.In a specific embodiment, the dianhydride monomer is3,3′,4,4′-biphenyltetracarboxylic dianhydride, pyromellitic dianhydride,or both.

In some aspects, the molar ratio of anhydride to total diamine is from0.4:1 to 1.6:1, 0.5:1 to 1.5:1, 0.6:1 to 1.4:1, 0.7:1 to 1.3:1, orspecifically from 0.8:1 to 1.2:1. In further aspects, the molar ratio ofdianhydride to multifunctional amine (e.g., triamine) is 2:1 to 140:1,3:1 to 130:1, 4:1 to 120:1, 5:1 to 110:1, 6:1 to 100:1, 7:1 to 90:1, orspecifically from 8:1 to 80:1. The polymer can also include amono-anhydride group, including for example 4-amino-1,8-naphthalicanhydride, endo-bicyclo[2.2.2]oct-5-ene-2,3-dicarboxylic anhydride,citraconic anhydride, trans-1,2-cyclohexanedicarboxylic anhydride,3,6-dichlorophthalic anhydride, 4,5-dichlorophthalic anhydride,tetrachlorophthalic anhydride 3,6-difluorophthalic anhydride,4,5-difluorophthalic anhydride, tetrafluorophthalic anhydride, maleicanhydride, 1-cyclopentene-1,2-dicarboxylic anhydride,2,2-dimethylglutaric anhydride 3,3-dimethylglutaric anhydride,2,3-dimethylmaleic anhydride, 2,2-dimethyl succinic anhydride,2,3-diphenylmaleic anhydride, phthalic anhydride, 3-methylglutaricanhydride, methyl succinic anhydride, 3-nitrophthalic anhydride,4-nitrophthalic anhydride, 2,3-pyrazinedicarboxylic anhydride, or3,4-pyridinedicarboxylic anhydride. Specifically, the mono-anhydridegroup is phthalic anhydride.

In another embodiment, the polymer compositions used to prepare theaerogels of the present invention include multifunctional amine monomerswith at least three primary amine functionalities. The multifunctionalamine may be a substituted or unsubstituted aliphatic multifunctionalamine, a substituted or unsubstituted aromatic multifunctional amine, ora multifunctional amine that includes a combination of an aliphatic andtwo aromatic groups, or a combination of an aromatic and two aliphaticgroups. A non-limiting list of possible multifunctional amines includepropane-1,2,3-triamine, 2-aminomethylpropane-1,3-diamine,3-(2-aminoethyl)pentane-1,5-diamine, bis(hexamethylene)triamine,N′,N′-bis(2-aminoethyl)ethane-1,2-diamine,N′,N′-bis(3-aminopropyl)propane-1,3-diamine,4-(3-aminopropyl)heptane-1,7-diamine,N′,N′-bis(6-aminohexyl)hexane-1,6-diamine, benzene-1,3,5-triamine,cyclohexane-1,3,5-triamine, melamine,N-2-dimethyl-1,2,3-propanetriamine, diethylenetriamine, 1-methyl or1-ethyl or 1-propyl or 1-benzyl-substituted diethylenetriamine,1,2-dibenzyldiethylenetriamine, lauryldiethylenetriamine,N-(2-hydroxypropyl)diethylenetriamine,N,N-bis(1-methylheptyl)-N-2-dimethyl-1,2,3-propanetriamine,2,4,6-tris(4-(4-aminophenoxy)phenyl)pyridine,N,N-dibutyl-N-2-dimethyl-1,2,3-propanetriamine,4,4′-(2-(4-aminobenzyl)propane-1,3-diyl)dianiline,4-((bis(4-aminobenzyl)amino)methyl)aniline,4-(2-(bis(4-aminophenethyl)amino)ethyl)aniline,4,4′-(3-(4-aminophenethyl)pentane-1,5-diyl)dianiline,1,3,5-tris(4-aminophenoxy)benzene (TAPOB),4,4′,4″-methanetriyltrianiline,N,N,N′,N′-Tetrakis(4-aminophenyl)-1,4-phenylenediamine, apolyoxypropylenetriamine, octa(aminophenyl)polyhedral oligomericsilsesquioxane, or combinations thereof. A specific example of apolyoxypropylenetriamine is JEFFAMINE® T-403 from Huntsman Corporation,The Woodlands, Tex. USA. In a specific embodiment, the aromaticmultifunctional amine may be 1,3,5-tris(4-aminophenoxy)benzene or4,4′,4″-methanetriyltrianiline. In some embodiments, the multifunctionalamine includes three primary amine groups and one or more secondaryand/or tertiary amine groups, for example,N′,N′-bis(4-aminophenyl)benzene-1,4-diamine.

Non-limiting examples of capping agents or groups include amines,maleimides, nadimides, acetylene, biphenylenes, norbornenes,cycloalkyls, and N-propargyl and specifically those derived fromreagents including 5-norbornene-2,3-dicarboxylic anhydride (nadicanhydride, NA), methyl-nadic anhydride, hexachloro-nadic anhydride,cis-4-cyclohexene-1,2-dicarboxylic anhydride,4-amino-N-propargylphthalimide, 4-ethynylphthalic anhydride, and maleicanhydride.

In some instances, the backbone of the aerogel polymer compositions caninclude further substituents. The substituents (e.g., oligomers,functional groups, etc.) can be directly bonded to the backbone orlinked to the backbone through a linking group (e.g., a tether or aflexible tether). In other embodiments, a compound or particles can beincorporated (e.g., blended and/or encapsulated) into the polymerstructure without being covalently bound to the polymer structure. Insome instances, the incorporation of the compound or particles can beperformed during the any step of the reaction process. In someinstances, particles can aggregate, thereby producing polyamic amide orpolyimide having domains with different concentrations of thenon-covalently bound compounds or particles.

In one instance, an aerogels of the present invention can include atleast 5 wt. % of the polyamic amide polymer based on the total weight ofthe polymer aerogel. In one particular instance, an aerogel of thepresent invention can include 5 wt. % to 50 wt. % of the polyamic amidepolymer based on the total weight of the polymer aerogel. In anotherinstance, an aerogel of the present invention can include 5 wt. % to 25wt. % of the polyamic amide polymer based on the total weight of thepolymer aerogel. An aerogel of the present invention can include 5, 6,7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 21, 22, 23, 24, 25,26, 27, 28, 29, 30, 31, 32, 33, 34, 35, 36, 37, 38, 39, 40, 41, 42, 43,44, 45, 46, 47, 48, 49, or 50 wt. % of the polyamic amide polymer basedon the total weight of the polymer aerogel.

E. Preparation of Aerogels

Aerogels of the present disclosure can be made using a multi-stepprocess that includes 1) preparation of the polyamic amide gel, 2)solvent exchange, and 3) drying of the polymeric solution to form theaerogel. These process steps are discussed in more detail below.

FIG. 1 is a non-limiting reaction schematic showing a conventionalsynthesis of a polyimide polymer that generate a polyisoimide byproduct.Diamine 100 is mixed with dianhydride 102 under reaction conditions 104to form an polyamic acid intermediate 106 that is further treated with atertiary amine and dehydration agent under reaction conditions 108 toform polyimide 110 and polyisoimide 112. In contrast to the conventionalsynthesis, the method of the present invention produces a copolymerhaving a polyimide repeating unit and a polyamic amide repeating unit.FIG. 2 is a non-limiting reaction schematic showing in anotherembodiment the synthesis of a polyimide polymer including polyamic amideinstead of polyisoimide. Polyamic acid intermediate 106 can be treatedwith a nitrogen containing hydrocarbon containing a secondary andtertiary amine and a dehydration agent under reaction conditions 200 toform polyimide 110 and polyamic amide 202.

1. Polyamic Amide Gels

The method to prepare a polyamic amide can include (a) providing atleast one diamine compound to a solvent to form a solution; (b)providing at least one dianhydride compound to the solution of step (a)under conditions sufficient to form a polyamic acid solution; (c)providing a secondary amine to the polyamic acid solution; (d)subjecting the mixture of step (c) to conditions suitable to produce apolymer matrix solution including a polyamic amide; and (e) subjectingthe polymer matrix solution to conditions sufficient to form an aerogel.As discussed above, numerous acid monomers, diamino monomers, andmultifunctional amine monomers can be used to synthesize a polyamicamide having minimal or no cross-linking. In one aspect of the currentinvention, one or more diamino monomers and one or more multifunctionalamine monomers are premixed in one or more solvents and then treatedwith one or more dianhydrides (e.g., di-acid monomers) that are added insequentially smaller amounts at pre-defined time increments whilemonitoring the viscosity. The desired viscosity of the polymerizedsolution can range from 50 to 20,000 cP or specifically 500 to 5,000 cP.By performing the reaction using incremental addition of dianhydridewhile monitoring viscosity, a non-crosslinked aerogel can be prepared.For instance, a triamine monomer (23 equiv.) can be added to the solventto give a 0.0081 molar solution. To the solution a first diamine monomer(280 equiv.) can be added, followed by second diamine monomer (280equiv.). Next a dianhydride (552 total equiv.) can be added insequentially smaller amounts at pre-defined time increments whilemonitoring the viscosity. The dianhydride can be added until theviscosity reaches 1,000 to 1,500 cP. For example, a first portion ofdianhydride can be added, the reaction can be stirred (e.g., for 20minutes), a second portion of dianhydride can be added, and a sample ofthe reaction mixture was then analyzed for viscosity. After stirring foradditional time (e.g., for 20 minutes), a third portion of dianhydridecan be added, and a sample can be taken for analysis of viscosity. Afterfurther stirring for a desired period of time (e.g., 10 hours to 12hours), a mono-anhydride (96 equiv.) can be added. After having reachedthe target viscosity, the reaction mixture can be stirred for a desiredperiod of time (e.g., 10 hours to 12 hours) or the reaction is deemedcompleted. After a desired amount of time (e.g., about 2 hours), theproduct can be isolated (e.g., filtered), after which a nitrogencontaining hydrocarbon (828 equiv.) and dehydration agent (1214 equiv.)can be added.

The reaction solvent can be dimethylsulfoxide, diethylsulfoxide,N,N-dimethylformamide, N,N-diethylformamide, N,N-dimethylacetamide,N,N-diethylacetamide, N-methyl-2-pyrrolidone, 1-methyl-2-pyrrolidinone,N-cyclohexyl-2-pyrrolidone, 1,13-dimethyl-2-imidazolidinone,diethyleneglycoldimethoxyether, o-dichlorobenzene, phenols, cresols,xylenol, catechol, butyrolactones, hexamethylphosphoramide, or mixturesthereof. The reaction solvent and other reactants can be selected basedon the compatibility with the materials and methods applied i.e. if thepolymerized polyamic amide gel is to be cast onto a support film,injected into a moldable part, or poured into a shape for furtherprocessing into a workpiece. In a specific embodiment, the reactionsolvent is dimethylsulfoxide.

In some aspects, a chemical curing system suitable for driving theconversion of polymer precursor to the polyamic amide or polyimide statecan be employed. Chemical catalysts can include nitrogen containinghydrocarbons. Non-limiting examples of such compounds include compoundscontaining at least one secondary amine. In one particular instance, anorganic compound having a secondary and a tertiary amine, such as2-methyl imidazole or 2-ethyl-4-methylimidazole can be used as achemical catalyst. In some embodiments, the secondary amines can be usedin combination with other chemical catalysts such as pyridine,methylpyridines, quinoline, isoquinoline,1,8-diazabicyclo[5.4.0]undec-7-ene (DBU), DBU phenol salts, carboxylicacid salts of DBU, triethylenediamine, carboxylic acid slats oftriethylenediamine, lutidine, N-methylmorpholine, triethylamine,tripropylamine, tributylamine, other trialkylamines, or combinationsthereof. Any dehydrating agent suitable for amidation can be used in themethods of the present invention. Dehydrating agents may include aceticanhydride, propionic anhydride, n-butyric anhydride, benzoic anhydride,trifluoroacetic anhydride, oxalyl chloride, thionyl chloride, phosphorustrichloride, dicyclohexylcarbodiimide, 1,1′-carbonyldiimidazole (CDI),di-tert-butyl dicarbonate (Boc₂O), or combinations thereof. Amidationcan also be achieved by using standard peptide coupling reagents such asbenzotriazol-1-yl-oxytripyrrolidinophosphonium hexafluorophosphate(PyBOP) or1-[Bis(dimethylamino)methylene]-1H-1,2,3-triazolo[4,5-b]pyridinium3-oxid hexafluorophosphate (HATU) in the presence of a base such asN,N-diisopropylethylamine (DIPEA), and a solvent, such as DMF and thelike.

While keeping the above in mind, the introduction of macropores into theaerogel polymeric matrix, as well as modifying or tuning the amount ofsuch macropores present, can be performed in the manner described abovein the Summary of the Invention Section as well as throughout thisspecification. In one non-limiting manner, the formation of macroporesvs smaller mesopores and micropores can be primarily controlled bycontrolling the polymer/solvent dynamics during gel formation. By doingso, the pore structure can be controlled, and the quantity and volume ofmacroporous, mesoporous, microporous cells can be controlled. Forexample, a curing additive that reduces the resultant polyimidesolubility, such as 1,4-diazabicyclo[2.2.2]octane, produces a polyimidecontaining a higher number of macropores compared to another curingadditive that improves the resultant polymer solubility, such astrimethylamine. In another example, using the same dianhydride such asBPDA but increasing the ratio of rigid amines incorporated into thepolymer backbone such as p-PDA as compared to more flexible diaminessuch as 4,4′-ODA, the formation of macropores as compared to smallermesopores and micropores can be controlled.

In some embodiments, the polyamic amide solution can be cast onto acasting sheet covered by a support film for a period of time. In certainembodiments, the casting sheet is a polyethylene terephthalate (PET)casting sheet. After a passage of time, the polymerized gel can beremoved from the casting sheet and prepared for the solvent exchangeprocess.

2. Solvent Exchange

After the polyamic amide gel is synthesized, it can be subjected to asolvent exchange where the reaction solvent is exchanged for a moredesirable second solvent. The original solvent can be exchanged with asecond solvent having a higher volatility than the first solvent andrepeated with various solvents. By way of example, the polymerized gelcan be placed inside of a pressure vessel and submerged in a mixturethat includes the reaction solvent and the second solvent. Then, a highpressure atmosphere can be created inside of the pressure vessel therebyforcing the second solvent into the polymerized gel and displacing aportion of the reaction solvent. Alternatively, the solvent exchangestep can be conducted without the use of a high pressure environment. Itmay be necessary to conduct a plurality of rounds of solvent exchange.

The time necessary to conduct the solvent exchange can vary dependingupon the type of polymer undergoing the exchange as well as the reactionsolvent and second solvent being used. In one embodiment, each solventexchange can range from 1 to 168 hours or any period time there betweenincluding 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18,19, 20, 21, 22, 23, 24, 25, 26, 27, 28, 29, 30, 31, 32, 33, 34, 35, 36,37, 38, 39, 40, 41, 42, 43, 44, 45, 46, 47, 48, 49, 50, 51, 52, 53, 54,55, 56, 57, 58, 59, 60, 61, 62, 63, 64, 65, 66, 67, 68, 69, 70, 71, 72,73, 74, 75, 76, 77, 78, 79, 80, 81, 82, 83, 84, 85, 86, 87, 88, 89, 90,91, 92, 93, 94, 95, 96, 97, 98, 99, 100, 101, 102, 103, 104, 105, 106,107, 108, 109, 110, 111, 112, 113, 114, 115, 116, 117, 118, 119, 120,121, 122, 123, 124, 125, 126, 127, 128, 129, 130, 131, 132, 133, 134,135, 136, 137, 138, 139, 140, 141, 142, 143, 144, 145, 146, 147, 148,149, 150, 151, 152, 153, 154, 155, 156, 157, 158, 159, 160, 161, 162,163, 164, 165, 166, or 167 hours. In another embodiment, each solventexchange can take approximately 30 minutes. Exemplary second solventsinclude methanol, ethanol, 1-propanol, 2-propanol, 1-butanol, 2-butanol,isobutanol, tert-butanol, 3-methyl-2-butanol, 3,3-dimethyl-2-butanol,2-pentanol, 3-pentanol, 2,2-dimethylpropan-1-ol, cyclohexanol,diethylene glycol, cyclohexanone, acetone, acetyl acetone, 1,4-dioxane,diethyl ether, dichloromethane, trichloroethylene, chloroform, carbontetrachloride, water, and mixtures thereof. In a specific embodiment,the second solvent is acetone. In certain non-limiting embodiments, thesecond solvent can have a suitable freezing point for performingsupercritical or subcritical drying steps. For example tert-butylalcohol has a freezing point of 25.5° C. and water has a freezing pointof 0° C. under one atmosphere of pressure. Alternatively, and asdiscussed below, however, the drying can be performed without the use ofsupercritical or subcritical drying steps, such as by evaporative dryingtechniques.

The temperature and pressure used in the solvent exchange process can bevaried. The duration of the solvent exchange process can be adjusted byperforming the solvent exchange at a varying temperatures or atmosphericpressures, or both, provided that the pressure and temperature insidethe pressure vessel does not cause either the first solvent or thesecond solvent to leave the liquid phase and become gaseous phase, vaporphase, solid phase, or supercritical fluid. Generally, higher pressuresand/or temperatures decrease the amount of time required to perform thesolvent exchange, and lower temperatures and/or pressures increase theamount of time required to perform the solvent exchange.

3. Cooling and Drying

In some embodiments after solvent exchange, the polymerized gel can bedried. The drying step can include supercritical drying, subcriticaldrying, thermal drying, evaporative air-drying, or any combinationthereof. In some embodiments, the polymerized gel can be exposed tosupercritical drying. In this instance the solvent in the gel can beremoved by supercritical CO2 extraction.

In another embodiment after solvent exchange, the polymerized gel can beexposed to subcritical drying. In this instance, the gel can be cooledbelow the freezing point of the second solvent and subjected to a freezedrying or lyophilization process to produce the aerogel. For example, ifthe second solvent is water, then the polymerized gel is cooled to below0° C. After cooling, the polymerized gel is subjected to a vacuum for aperiod of time wherein the second solvent is allowed to sublime.

In still another embodiment after solvent exchange, the polymerized gelcan be exposed to subcritical drying with optional heating after themajority of the second solvent has been removed through sublimation. Inthis instance, the partially dried gel material is heated to atemperature near, or above, the boiling point of the second solvent fora period of time. The period of time can range from a few hours toseveral days, although a typical period of time is approximately 4hours. During the sublimation process, a portion of the second solventpresent in the polymerized gel has been removed, leaving a gel that canhave macropores, mesopores, or micropores, or any combination thereof orall of such pore sizes. After the sublimation process is complete, ornearly complete, the aerogel has been formed.

In yet another embodiment after solvent exchange, the polymerized gelcan be dried under ambient conditions, for example, by removing thesolvent under a stream of gas (e.g., air, anhydrous gas, inert gas(e.g., nitrogen (N₂) gas), etc. Still further, passive drying techniquescan be used such as simply exposing the gel to ambient conditionswithout the use of a gaseous stream. In this instance, the solvent inthe gel is removed by evaporation and pore collapse is prevented by theaerogel network. The drying may also be assisted by heating orirradiating with electromagnetic radiation.

F. Articles of Manufacture

The open-cell aerogel of the present invention can be included in anarticle of manufacture. For example, an article of manufacture caninclude a branched polyamic amide matrix with less than 5% by weight ofcrosslinked polymers. In some embodiments, the article of manufacture isa thin film, monolith, wafer, blanket, core composite material,substrate for radiofrequency antenna, a sunscreen, a sunshield, aradome, insulating material for oil and/or gas pipeline, insulatingmaterial for liquefied natural gas pipeline, insulating material forcryogenic fluid transfer pipeline, insulating material for apparel,insulating material for aerospace applications, insulating material forbuildings, cars, and other human habitats, insulating material forautomotive applications, insulation for radiators, insulation forducting and ventilation, insulation for air conditioning, insulation forheating and refrigeration and mobile air conditioning units, insulationfor coolers, insulation for packaging, insulation for consumer goods,vibration dampening, wire and cable insulation, insulation for medicaldevices, support for catalysts, support for drugs, pharmaceuticals,and/or drug delivery systems, aqueous filtration apparatus, oil-basedfiltration apparatus, and solvent-based filtration apparatus.

1. Fluid Filtration Applications

In some embodiments, the open-cell aerogel of the present invention canbe used in fluid filtration systems and apparatus. A feed fluid can becontacted with the branched polyamic amide aerogel such that some, allor, substantially all, of the impurities and/or desired substances areremoved from the feed fluid to produce a filtrate essentially devoid ofthe impurities and/or desired substances. The filtrate, impurities,and/or desired substances can be collected, stored, transported,recycled, or further processed. The polyamic amide aerogel can befurther processed to release the impurities and/or desired substancesfrom the aerogel.

The polyamic amide aerogel described herein can be used in or withfiltration apparatuses known in the art. Non-limiting examples offiltration apparatuses and applications include gas filters such as, butnot limited to, building air filters, automotive cabin air filters,combustion engine air filters, aircraft air filters, satellite airfilters, face mask filters, diesel particulate filters, in-line gasfilters, cylinder gas filters, soot filters, pressure swing absorptionapparatus, etc. Additional non-limiting examples of filtrationapparatuses and applications include solvent filtration systems, columnfiltration, chromatography filtration, vacuum flask filtration,microfiltration, ultrafiltration, reverse osmosis filtration,nanofiltration, centrifugal filtration, gravity filtration, cross flowfiltration, dialysis, hemofiltration, hydraulic oil filtration,automotive oil filtration, etc. Further, non-limiting examples of thepurpose of filtration includes sterilization, separation, purification,isolation, etc.

A fluid for filtration (“feed”) and a filtrate can be any fluid. Thefluid can be a liquid, gas, supercritical fluid, emulsion, or mixturethereof. In some instances, the liquid can be aqueous, non-aqueous,organic, non-organic, biological in origin, or a mixture thereof. Insome instances, the gas can include air, nitrogen, oxygen, an inert gas,or mixtures thereof. In some instances, the liquid can contain solidsand/or other fluids or be an emulsion. In particular instances theemulsion is a water-oil emulsion, an oil-water emulsion, a water-solventemulsion, a solvent-water emulsion, an oil-solvent emulsion, or asolvent-oil emulsion. As non-limiting examples, the liquid can be water,blood, plasma, an oil, a solvent, air, or mixtures thereof. The solventcan be an organic solvent. Water can include water, any form of steamand supercritical water.

In some instances, the fluid can contain impurities. Non-limitingexamples of impurities include solids, liquids, gases, supercriticalfluids, objects, compounds, and/or chemicals, etc. What is defined as animpurity may be different for the same feed fluid depending on thefiltrate desired. In some embodiments, one or more aerogels can be usedto remove impurities. Non-limiting examples of impurities in water caninclude ionic substances such as sodium, potassium, magnesium, calcium,fluoride, chloride, bromide, sulfate, sulfite, nitrate, nitrites,cationic surfactants, and anionic surfactants, metals, heavy metals,suspended, partially dissolved, or dissolved oils, organic solvents,nonionic surfactants, defoamants, chelating agents, microorganisms,particulate matter, etc. Non-limiting examples of impurities in bloodcan include red blood cells, white blood cells, antibodies,microorganisms, water, urea, potassium, phosphorus, gases, particulatematter, etc. Non-limiting examples of impurities in oil can includewater, particulate matter, heavy and/or light weight hydrocarbons,metals, sulfur, defoamants, etc. Non-limiting examples of impurities insolvents can include water, particulate matter, metals, gases, etc.Non-limiting impurities in air can include water, particulate matter,microorganisms, liquids, carbon monoxide, sulfur dioxide, etc.

In some instances, the feed fluid can contain desired substances.Desired substances can be, but are not limited to, solids, liquids,gases, supercritical fluids, objects, compounds, and/or chemicals, etc.In some embodiments, one or more aerogels can be used to concentrate orcapture a desired substance, or remove a fluid from a desired substance.Non-limiting examples of desired substances in water can include ionicsubstances such as sodium, potassium, magnesium, calcium, fluoride,chloride, bromide, sulfate, sulfite, nitrate, nitrites, cationicsurfactants, and anionic surfactants, metals, heavy metals, suspended,partially dissolved, or dissolved oils, organic solvents, nonionicsurfactants, chelating agents, microorganisms, particulate matter, etc.Non-limiting examples of desired substances in blood can include redblood cells, white blood cells, antibodies, lipids, proteins, etc.Non-limiting examples of desired substances in oil can includehydrocarbons of a range of molecular weights, gases, metals, defoamants,etc. Non-limiting examples of desired substances in solvents can includeparticulate matter, fluids, gases, proteins, lipids, etc. Non-limitingexamples of desired substances in air can include water, fluids, gases,particulate matter, etc.

FIGS. 3, 4, and 5 are non-limiting schematics of a system 300 used tocarry out a filtration of a fluid using an aerogel. System 300 caninclude a separation zone 302. The materials, size, and shape of theseparation zone 302 can be determined using standard engineeringpractice to achieve the desired flow rates and contact time. Theseparation zone 302 is capable of holding or may be made of one or moreaerogels and includes a feed fluid inlet 304 (inlet) and/or a filtrateoutlet 306 (outlet). In some instances, the separation zone is madeentirely of one or more branched polyamic amide aerogels or one or morebranched polyamic amide aerogels in or around a supporting structure.The feed fluid 308 can be introduced to the separation zone 302 throughthe inlet 304 (See, FIGS. 3 and 4 ) or through direct contact with theseparation zone 302 (FIG. 5 ). In some embodiments, the feed fluid 308can be received under greater or reduced pressure than ambient pressure.Introduction of the feed fluid 308 into separation zone 302 can be at arate sufficient to allow optimum contact of the feed fluid with the oneor more aerogels. Contact of the feed fluid 308 with the aerogel canallow the feed fluid to be filtered by the aerogel, which results in thefiltrate 310. The filtrate 310 can have less impurity and/or desiredsubstance when compared with the feed fluid 308. In certain aspects, thefiltrate 310 can be essentially free of the impurity and/or the desiredsubstance. The filtrate 310 can exit the separation zone 302 via theoutlet 306 (See, FIGS. 3 and 5 ) or through directly exiting theseparation zone 302 (See, FIG. 4 ). In some instances, the filtrate canbe recycled back to a separation zone, collected, stored in a storageunit, etc. In some instances, one or more aerogels can be removed and/orreplaced from the separation zone. In some instances, the filtrate 310can be collected and/or removed from the separation zone 302 without thefiltrate 310 flowing through an outlet 306. In some instances, theimpurities and/or desired substance can be removed from the separationzone 302. As one non-limiting example, removal of the impurities and/ordesired substances from the separation zone using counter-current flowof the fluids through the separation zone.

The filtration conditions in the separation zone 302 can be varied toachieve a desired result (e.g., removal of substantially all of theimpurities and/or desired substance from the feed fluid). The filtrationconditions include temperature, pressure, fluid feed flow, filtrateflow, or any combination thereof. Filtration conditions are controlled,in some instances, to produce streams with specific properties. Theseparation zone 302 can also include valves, thermocouples, controllers(automated or manual controllers), computers or any other equipmentdeemed necessary to control or operate the separation zone. The flow ofthe feed fluid 304 can be adjusted and controlled to maintain optimumcontact of the feed fluid with the one or more aerogel. In someembodiments, computer simulations can be used to determine flow ratesfor separation zones of various dimensions and various aerogels.

The compatibility of an aerogel with a fluid and/or filtrationapplication can be determined by methods known in the art. Someproperties of an aerogel that may be determined to assess thecompatibility of the aerogel may include, but is not limited to: thetemperature and/or pressures that the aerogel melts, dissolves,oxidizes, reacts, degrades, or breaks; the solubility of the aerogel inthe material that will contact the aerogel; the flow rate of the fluidthrough the aerogel; the retention rate of the impurity and/or desiredproduct form the feed fluid; etc.

2. Radiofrequency (RF) Applications

Due to their low density, mechanical robustness, light weight, and lowdielectric properties, the branched polyamic amide aerogels can be usedin radiofrequency (RF) applications. The use of branched polyamic amideaerogels in RF applications enables the design of thinner substrates,lighter weight substrates and smaller substrates. Non-limiting examplesof radiofrequency applications include a substrate for a RF antenna, asunshield for a RF antenna, a radome, or the like. Antennas can includeflexible and/or rigid antennas, broadband planar circuited antennas(e.g. a patch antennas, an e-shaped wideband patch antenna, anelliptically polarized circular patch antenna, a monopole antenna, aplanar antenna with circular slots, a bow-tie antenna, an inverted-Fantenna and the like). In the antenna design, the circuitry can beattached to a substrate that includes the branched polyamic amideaerogel and/or a mixture of the branched polyamic amide aerogel andother components such as other polymeric materials including adhesivesor polymer films, organic and inorganic fibers (e.g. polyester,polyamide, polyimide, carbon, glass fibers), other organic and inorganicmaterials including silica aerogels, polymer powder, glassreinforcement, etc. The use of branched polyamic amide aerogels inantennas enables the design substrates with higher throughput. Inaddition, the branched polyamic amide aerogels have coefficient oflinear thermal expansion (CTE) similar to aluminum and copper (e.g., CTEof 23 ppm/K and 17 ppm/K), and is tunable through choice of monomer tomatch CTE of other desirable materials. In some embodiments, the aerogelcan be used in sunshields and/or sunscreens used to protect RF antennasfrom thermal cycles due to their temperature insensitivity and RFtransparency. In certain embodiments, the aerogel can be used as amaterial in a radome application. A radome is a structural, weatherproofenclosure that protects a microwave (e.g., radar) antenna. Branchedpolyamic amide aerogels can minimize signal loss due to their lowdielectric constant and also provide structural integrity due to theirstiffness.

EXAMPLES

The present invention will be described in greater detail by way ofspecific examples. The following examples are offered for illustrativepurposes only, and are not intended to limit the invention in anymanner.

A. Example 1 (Preparation of a Highly Branched Polyamic Amide)

A reaction vessel with a mechanical stirrer and a water jacket wasemployed. The flow of the water through the reaction vessel jacket wasadjusted to maintain temperature in the range of 20-28° C. The reactionvessel was charged with dimethylsulfoxide (DMSO) (108.2 lbs. 49.1 kg),and the mechanical stirrer speed was adjusted to 120-135 rpm.1,3,5-tris(4-aminophenoxy) benzene (TAPOB, 65.03 g) was added to thesolvent. To the solution was added 4,4′-diamino-2,2′-dimethylbiphenyl(DMB, 1,080.96 g), followed by 4,4′-oxydianiline (ODA, 1,018.73 g). Afirst portion of biphenyl-tetracarboxylic acid dianhydride (BPDA)(1,524.71 g) was added. After stirring for 20 minutes, a sample of thereaction mixture was analyzed for viscosity. A second portion of BPDA(1,420.97 g) was added, and the reaction mixture was stirred for 20additional minutes. A sample of the reaction mixture was analyzed forviscosity. A third portion of BPDA (42.81 g) was added, and the reactionmixture was stirred for 20 additional minutes. A sample of the reactionmixture was analyzed for viscosity. After stirring for 8 hours, phthalicanhydride (PA, 77.62 g) was added. The resulting reaction mixture wasstirred until no more solid was visible. After 2 hours, the product wasremoved from the reaction vessel, filtered, and weighed. Structures ofthe starting materials are shown below:

B. Example 2 (Preparation of a Highly Branched Polyamic Amide AerogelFilm)

The resin (10,000 grams) prepared in Example 1 was mixed with2-methylimidazole (250 grams) for five minutes. Benzoic anhydride (945grams) was added, and the solution mixed an additional five minutes.After mixing, the resultant solution was poured onto a moving polyestersubstrate that was heated in an oven at 100° C. for 30 seconds. Thegelled film was collected and placed into an acetone bath. Afterimmersion for 24 hours, the acetone bath was exchanged for freshacetone. The soak and exchange process was repeated six times. After thefinal exchange, the gelled film was removed. The acetone solvent wasevaporated under a stream of air at room temperature, and subsequentlydried for 2 hrs hours at 200° C. The final recovered aerogel part hadopen-cell structure as observed by scanning electron microscopy (SEM)performed on a Phenom Pro Scanning Electron Microscope (Phenom-World,the Netherlands), exhibited a density of 0.20 g/cm³ and porosity of >85%as measured according to ASTM D4404-10 with a Micromeritics® AutoPore V9605 Automatic Mercury Penetrometer (Micromeritics® InstrumentCorporation, U.S.A.). The final recovered film exhibited a tensilestrength and elongation of 1200 psi (8.27 MPa) and 14%, respectively, atroom temperature as measured according to ASTM D882-02.

C. Example 3 (Preparation of a Highly Branched Polyamic Amide)

The reaction vessel as described in Example 1 was charged withdimethylsulfoxide (DMSO) (108.2 lbs. 49.1 kg), and the mechanicalstirrer speed was adjusted to 120-135 rpm. 1,3,5-tris(4-aminophenoxy)benzene (TAPOB, 65.93 g) was added to the solvent. To the solution wasadded 4,4′-diamino-2,2′-dimethylbiphenyl (DMB, 1,081.64 g), followed by4,4′-oxydianiline (ODA, 1,020.23 g). A first portion of BPDA (1,438.35g) was added. After stirring for 20 minutes, a sample of the reactionmixture was analyzed for viscosity. A second portion of BPDA (1,407.77g) was added, and the reaction mixture was stirred for 20 additionalminutes. A sample of the reaction mixture was analyzed for viscosity. Athird portion of BPDA (74.35 g) was added, and the reaction mixture wasstirred for 20 additional minutes. A sample of the reaction mixture wasanalyzed for viscosity. After stirring for 8 hours, phthalic anhydride(PA, 174.00 g) was added. The resulting reaction mixture was stirreduntil no more solid was visible. After 2 hours, the product was removedfrom the reaction vessel, filtered, and weighed. D. Example 4(Preparation of a Highly Branched Polyamic Amide Aerogel Monolith)

The resin (16,49 kilograms) prepared in Example 3 was mixed with2-methylimidazole (1.13 kilograms) for five minutes. Benzoic anhydride(3.44 kilograms) was added, and the solution mixed an additional fiveminutes. After mixing, the resultant solution was poured into a square16″×16″ mold, and then left overnight at room temperature. The gelledshape was removed from the mold, and placed into an acetone bath. Afterimmersion for 24 hours, the acetone bath was exchanged with freshacetone. The soak and exchange process was repeated five times. Afterthe final exchange, the gelled film was removed. The acetone solvent wasevaporated under a stream of air at room temperature, and subsequentlydried for 1.5 hrs hours at 200° C. The final recovered aerogel part hadopen-cell structure as observed by scanning electron microscopy (SEM)performed on a Phenom Pro Scanning Electron Microscope (Phenom-World,the Netherlands), exhibited a density of 0.14 g/cm³ and porosity of >85%as measured according to ASTM D4404-10 with a Micromeritics® AutoPore V9605 Automatic Mercury Penetrometer (Micromeritics® InstrumentCorporation, U.S.A.). The final recovered film exhibited a compressionstrength of 230 psi at room temperature as measured according to ASTMD395-14.

E. Example 5 (Preparation of a Highly Branched Polyamic Acid)

TAPOB (about 2.86 g) was added to the reaction vessel charged with about2,523.54 g DMSO as described in Example 1. To the solution was added afirst portion of DMB (about 46.75 g), followed by a first portion of ODA(about 44.09 g). After stirring for about 20 minutes, a first portion ofBPDA (about 119.46 g) was added. After stirring for about 20 minutes,TAPOB (about 2.86 g), DMB (about 46.75 g), and ODA (about 44.09 g) wereadded. After stirring for about 20 minutes, BPDA (about 119.46 g) wasadded. After stirring for about 20 minutes, TAPOB (about 2.86 g), DMB(about 46.75 g), and ODA (about 44.09 g) were added. After stirring forabout 20 minutes, BPDA (about 119.46 g) was added. After stirring forabout 8 hours, PA (about 50.12 g) was added. The resulting reactionmixture was stirred until no more solids were visible. After about 2hours, the product was removed from the reaction vessel, filtered, andweighed.

F. Example 6 (Preparation of a Highly Branched Aerogel Monolith byFreeze Drying)

The resin (about 400 grams) prepared in Example 5 was mixed with2-methylimidazole (about 53.34 grams) for five minutes and then benzoicanhydride (about 161.67 grams) for five minutes. After mixing, theresultant solution was poured into a square 3″×3″ mold and placed in anoven at 75° C. for 30 minutes and then left overnight at roomtemperature. The gelled shape was removed from the mold, and placed intoan acetone bath. After immersion for 24 hours, the acetone bath wasexchanged with fresh acetone. The soak and exchange process was repeatedfive times. After the final exchange, the bath was replaced withtertiary butyl alcohol. After immersion for 24 hours, the tertiary butylalcohol bath was exchanged for fresh tertiary butyl alcohol. The soakand exchange process was repeated three times The part was subsequentlyfrozen on a shelf freezer, and subjected to subcritical drying for 96hours in at 5° C., followed by drying in vacuum at 50° C. for 48 hours.The final recovered aerogel part had open-cell structure as observed byscanning electron microscopy (SEM) performed on a Phenom Pro ScanningElectron Microscope (Phenom-World, the Netherlands), exhibited a densityof 0.15 g/cm³ and porosity of 92.2% as measured according to ASTMD4404-10 with a Micromeritics® AutoPore V 9605 Automatic MercuryPenetrometer (Micromeritics® Instrument Corporation, U.S.A.). Thedistribution of pore sizes were measured according to ASTM D4404-10using a Micromeritics® AutoPore V 9605 Automatic Mercury Penetrometer(Micromeritics® Instrument Corporation, U.S.A.), and the distribution ofpore diameters is shown in FIG. 6 . Notably, and as illustrated in FIG.6 , the produced aerogel includes macropores in its polymeric matrix. Italso includes mesopores in the polymeric matrix.

G. Example 7 (Preparation of a Highly Branched Polyamic Acid)

TAPOB (about 2.05 g) was added to the reaction vessel charged with about2,776.57 g DMSO as described in Example 1. To the solution was added afirst portion of DMB (about 33.54 g), followed by a first portion of ODA(about 31.63 g). After stirring for about 20 minutes, a first portion ofPMDA (about 67.04 g) was added. After stirring for about 20 minutes,TAPOB (about 2.05 g), DMB (about 33.54 g), and ODA (about 31.63 g) wereadded. After stirring for about 20 minutes, PMDA (about 67.04 g) wasadded. After stirring for about 20 minutes, TAPOB (about 2.05 g), DMB(about 33.54 g), and ODA (about 31.63 g) were added. After stirring forabout 20 minutes, PMDA (about 67.04 g) was added. After stirring forabout 8 hours, PA (about 18.12 g) was added. The resulting reactionmixture was stirred until no more solids were visible. After about 2hours, the product was removed from the reaction vessel, filtered, andweighed.

H. Example 8 (Preparation of a Highly Branched Aerogel Monolith byFreeze Drying)

The resin (about 400 grams) prepared in Example 7 was mixed with2-methylimidazole (about 40.38 grams) for five minutes and then benzoicanhydride (about 122.38 grams) for five minutes. After mixing, theresultant solution was poured into a square 3″×3″ mold and placed in anoven at 75° C. for 30 minutes and then left overnight at roomtemperature. The gelled shape was removed from the mold, and placed intoan acetone bath. After immersion for 24 hours, the acetone bath wasexchanged with fresh acetone. The soak and exchange process was repeatedfive times. After the final exchange, the bath was replaced withtertiary butyl alcohol. After immersion for 24 hours, the tertiary butylalcohol bath was exchanged for fresh tertiary butyl alcohol. The soakand exchange process was repeated three times The part was subsequentlyfrozen on a shelf freezer, and subjected to subcritical drying for 96hours in at 5° C., followed by drying in vacuum at 50° C. for 48 hours.The final recovered aerogel part had an open-cell structure as observedby scanning electron microscopy (SEM) performed on a Phenom Pro ScanningElectron Microscope (Phenom-World, the Netherlands), exhibited a densityof 0.23 g/cm³ and porosity of 82.7% as measured according to ASTMD4404-10 with a Micromeritics® AutoPore V 9605 Automatic MercuryPenetrometer (Micromeritics® Instrument Corporation, U.S.A.). Thedistribution of pore sizes was measured according to ASTM D4404-10 usinga Micromeritics® AutoPore V 9605 Automatic Mercury Penetrometer(Micromeritics® Instrument Corporation, U.S.A.), and the distribution ofpore diameters is shown in FIG. 7 . Notably, and as illustrated in FIG.7 , the produced aerogel includes macropores in its polymeric matrix. Italso includes mesopores in the polymeric matrix. From the trend in thedata, it is believed that the aerogel contains some micropores.

I. Example 9 (Preparation of a Linear Polyamic Acid)

A reaction vessel was charged with about 776.42 g DMSO as described inExample 1. To the solution was added a first portion of ODA (about 12.76g). After stirring for about 20 minutes, a first portion of PMDA (about11.82 g) was added. After stirring for about 20 minutes, ODA (about12.76 g) was added. After stirring for about 20 minutes, PMDA (about11.82 g) was added. After stirring for about 20 minutes, ODA (about12.76 g) was added. After stirring for about 20 minutes, PMDA (about11.82 g) was added. After stirring for about 8 hours, PA (about 10.62 g)was added. The resulting reaction mixture was stirred until no moresolids were visible. After about 2 hours, the product was removed fromthe reaction vessel, filtered, and weighed.

J. Example 10 (Preparation of a Linear Aerogel Monolith by FreezeDrying)

The resin (about 400 grams) prepared in Example 9 was mixed with2-methylimidazole (about 53.38 grams) for five minutes and then benzoicanhydride (about 161.80 grams) for five minutes. After mixing, theresultant solution was poured into a square 3″×3″ mold and placed in anoven at 75° C. for 30 minutes and then left overnight at roomtemperature. The gelled shape was removed from the mold, and placed intoan acetone bath. After immersion for 24 hours, the acetone bath wasexchanged with fresh acetone. The soak and exchange process was repeatedfive times. After the final exchange, the bath was replaced withcyclohexane. After immersion for 24 hours, the cyclohexane bath wasexchanged for fresh cyclohexane. The soak and exchange process wasrepeated three times The part was subsequently frozen in a freezer, andsubjected to subcritical drying for 96 hours in at 5° C., followed bydrying in vacuum at 50° C. for 48 hours. The final recovered aerogelpart had open-cell structure as observed by scanning electron microscopy(SEM) performed on a Phenom Pro Scanning Electron Microscope(Phenom-World, the Netherlands), exhibited a density of 0.36 g/cm³ andporosity of 79.0% as measured according to ASTM D4404-10 with aMicromeritics® AutoPore V 9605 Automatic Mercury Penetrometer(Micromeritics® Instrument Corporation, U.S.A.). The distribution ofpore sizes was measured according to ASTM D4404-10 using aMicromeritics® AutoPore V 9605 Automatic Mercury Penetrometer(Micromeritics® Instrument Corporation, U.S.A.), and the distribution ofpore diameters is shown in FIG. 8 . Notably, and as illustrated in FIG.8 , the produced aerogel does not include a primarily macroporuouslystructured polymeric matrix. Rather, the matrix primarily includesmesopores in the polymeric matrix. From the trend in the data, it isbelieved that the aerogel contains some micropores.

K. Example 11 (FTIR Data)

FTIR spectral data was obtained for the Example 3 resin, the Example 4aerogel, and a comparative commercial polyimide aerogel (Kapton®polyimide aerogel from DuPont USA (Wilmington, Del., USA) by using aNicolet iS5 FT-IR spectrometer with an iD7 attenuated total reflectance(ATR) diamond crystal accessory (Thermo Scientific, Waltham, Mass.,USA). The diamond crystal was wiped down with isopropanol betweensamples. Use of the ATR allowed data collection from both solid andliquid samples with no sample preparation. The FTIR data is organized inTable 1.

TABLE 1 Comparative Commercial Absorption Vibration Example 3 Example 4Polyimide Group frequency mode Resin¹ Aerogel² Aerogel³ PolyamicAmide-Acid 2900-3200 COOH and NH₂ Present Absent Absent acid (PAA)Aromatic C—H 2900-3100 C—H stretch Present Present Present Carbonyl from1710-1720 C═O Present Overlap w/ Overlap w/ acid (COOH) Imide I Imide Istretch Amide I 1660-1665 C═O Present Absent Absent (CONH) stretch AmideII 1540-1565 C—NH Present Absent Absent Carboxylate 1330-1415 COO⁻ sym.Present Overlap w/ Overlap w/ ion stretch Imide II Imide II PolylmideImide I 2900-3100 C—H stretch Present Present Present Imide I 1770-1780C═O sym. Absent Present Present stretch Imide I 1720-1740 C═O asym.Overlap with Present Present stretch amic acid Imide II 1360-1380 C═NAbsent Present Present stretch Imide III 1070-1090 C—H Overlap withPresent Present bending DMSO Imide III 1120-1140 C—H Absent PresentPresent bending Imide IV 720-740 C═O Absent Present Present bendingIsoimide Isoimide 1805-1750 C═O Absent Overlap w/ Overlap w/ model ImideI Imide I compound⁴ Isoimide 1400-1425 C═N Absent Present Absent stretchIsoimide 890-905 C—O Overlap with Present Absent DMSO Amic AmideAmic-Amide 1415-1440 C═N Absent Present Absent model stretch compound⁵Amic-Amide 735-745 C—N Absent Present Absent ¹The gel/resin from Example3 was used. ²The monolith aerogel from Example 4 was used. ³Kapton ®polyimide aerogel from DuPont USA (Wilmington, DE, USA).⁴N-Phenyl-phthalisoimide was used as the isoimide model compound ascharacterized by Mochizuki et al. “Preparation and properties ofpolyisoimide as a polyimide-precursor.” Polymer journal 1994, 26. 3:315-323. ⁵N,N,N′,N′,-tetramethylphthalamide was used as the amic amidemodel compound. Model compound spectra were obtained from the NationalInstitute of Advanced Industrial Science and Technology (AIST) database,which can be found athttp://sdbs.db.aist.go.jp/sdbs/cgi-bin/direct_frame_top.cgi.

1. An aerogel comprising an open-cell structured polymer matrix thatincludes 5 wt. % to 50 wt. % of a polyamic amide polymer, based on thetotal weight of the aerogel, wherein the aerogel comprises pores and atleast 90% of the pore volume of the aerogel is made up of macropores;wherein the aerogel has a porosity of at least 50%, as measure accordingto ASTM D4404-10, wherein the aerogel has a density of 0.01 g/cm³ to 0.5g/cm³, and wherein the aerogel is thermally stable to resist browning at330° C.
 2. The aerogel of claim 1, wherein the pores have an averagepore diameter of 100 nanometers (nm) to 500 nm.
 3. The aerogel of claim1, wherein the aerogel includes 5 wt. % to 25 wt. % of the polyamicamide polymer based on the total weight of the aerogel.
 4. The aerogelof claim 1, wherein the aerogel has an elongation of 0.1% to 50%, asmeasured by ASTM D882-02.
 5. The aerogel of claim 1, wherein the aerogelhas a tensile strength of 100 psi to 2500 psi, as measured by ASTMD882-02.
 6. The aerogel of claim 1, wherein the polyamic amid polymerhas a repeating structural unit of

where each Z has the following structure:

where R₃, R₄, and R₅ are each individually a hydrogen (H) atom, an alkylgroup, or a substituted alkyl group, with the proviso that at least oneof R₃, R₄, and R₅ is an alkyl group, or a substituted alkyl group, X isa first organic group derived from the at least one diamine selectedfrom the group consisting of 4,4′-oxydianiline, 3,4′-oxydianiline,3,3-oxydianiline, p-phenylenediamine, m-phenylenediamine,o-phenylenediamine, diaminobenzanilide, 3,5-diaminobenzoic acid,3,3′-diaminodiphenylsulfone, 4,4′-diaminodiphenylsulfones,1,3-bis-(4-aminophenoxy)benzene, 1,3-bis-(3-aminophenoxy)benzene,1,4-bis-(4-aminophenoxy)benzene, 1,4-bis-(3-aminophenoxy)benzene,2,2-Bis[4-(4-aminophenoxy)phenyl]-hexafluoropropane,2,2-bis(3-aminophenyl)-1,1,1,3,3,3-hexafluoropropane,4,4′-isopropylidenedianiline,1-(4-aminophenoxy)-3-(3-aminophenoxy)benzene,1-(4-aminophenoxy)-4-(3-aminophenoxy)benzene,bis-[4-(4-aminophenoxy)phenyl]sulfones,2,2-bis[4-(3-aminophenoxy)phenyl]sulfones,bis-[4-(4-aminophenoxy]phenyl)ether,2,2′-bis-(4-aminophenyl)-hexafluoropropane, (6F-diamine),2,2′-bis-(4-phenoxyaniline)isopropylidene, meta-phenylenediamine,para-phenylenediamine, 1,2-diaminobenzene, 4,4′-diaminodiphenylmethane,2,2-bis(4-aminophenyl)propane, 4,4′diaminodiphenylpropane,4,4′-diaminodiphenylsulfide, 4,4′-diaminodiphenylsulfone,3,4′diaminodiphenylether, 4,4′-diaminodiphenylether,2,6-diaminopyridine, bis(3-aminophenyl)diethyl silane,4,4′-diaminodiphenyl diethyl silane, benzidine, dichlorobenzidine,3,3′-dimethoxybenzidine, 4,4′-diaminobenzophenone,N,N-bis(4-aminophenyl)-n-butylamine, N,N-bis(4-aminophenyl)methylamine,1,5-diaminonaphthalene, 3,3′-dimethyl-4,4′-diaminobiphenyl,4-aminophenyl-3-aminobenzoate, N,N-bis(4-aminophenyl)aniline,bis(p-beta-amino-t-butylphenyl)ether,p-bis-2-(2-methyl-4-aminopentyl)benzene,p-bis(1,1-dimethyl-5-aminopentyl)benzene,1,3-bis(4-aminophenoxy)benzene, m-xylenediamine, p-xylenediamine,4,4′-diaminodiphenyletherphosphine oxide, 4,4′-diaminodiphenylN-methylamine, 4,4′-diaminodiphenyl N-phenylamine, amino-terminalpolydimethylsiloxanes, amino-terminal polypropyleneoxides,amino-terminal polybutyleneoxides,4,4′-methylenebis(2-methylcyclohexylamine), 1,2-diaminoethane,1,3-diaminopropane, 1,4-diaminobutane, 1,5-diaminopentane,1,6-diaminohexane, 1,7-diaminoheptane, 1,8-diaminooctane,1,9-diaminononane, 1,10-diaminodecane, 4,4′-methylenebisbenzeneamine,2,2′-dimethylbenzidine, (also known as4,4′-diamino-2,2′-dimethylbiphenyl (DMB), bisaniline-p-xylidene,4,4′-bis(4-aminophenoxy)biphenyl, 3,3′-bis(4 aminophenoxy)biphenyl,4,4′-(1,4-phenylenediisopropylidene)bisaniline,4,4′-(1,3-phenylenediisopropylidene)bisaniline, and combinationsthereof, and and Y is a second organic group derived from the at leastone dianhydride selected from the group consisting of hydroquinonedianhydride, 3,3′,4,4′-biphenyltetracarboxylic dianhydride, pyromelliticdianhydride, 3,3′,4,4′-benzophenone-tetracarboxylic dianhydride,4,4′-oxydiphthalic anhydride, 3,3′,4,4′-diphenylsulfone-tetracarboxylicdianhydride, 4,4′-(4,4′-isopropylidenediphenoxy)bis(phthalic anhydride),2,2-bis(3,4-dicarboxyphenyl)propane dianhydride,4,4′-(hexafluoroisopropylidene)diphthalic anhydride,bis(3,4-dicarboxyphenyl)sulfoxide dianhydride, polysiloxane-containingdianhydride, 2,2′,3,3′-biphenyltetracarboxylic dianhydride,2,3,2′,3′-benzophenonetetraearboxylic dianhydride,3,3′,4,4′-benzophenonetetraearboxylic dianhydride,naphthalene-2,3,6,7-tetracarboxylic dianhydride,naphtholene-1,4,5,8-tetracarboxylic dianhydride, 4,4′-oxydiphthalicdianhydride, 3,3′,4,4′-biphenylsulfone tetracarboxylic dianhydride,3,4,9,10-peryene tetracarboxylic dianhydride,bis(3,4-dicarboxyphenyl)sulfide dianhydride,bis(3,4-dicarboxypheny)methane dianhydride,2,2-bis(3,4-dicarboxyphenyl)propane dianhydride,2,2-bis(3,4-dicarboxyphenyl)hexafluoropropene,2,6-dichloronaphthalene-1,4,5,8-tetracarboxylic dianhydride,2,7-dichloronapthalene-1,4,5,8-tetracarboxylic dianhydride,2,3,6,7-tetrachloronaphthalene-1,4,5,8-tetracarboxylic dianhydride,phenanthrene-8,9,10-tetracarboxylic dianhydride,pyrazine-2,3,5,6-tetracarboxylic dianhydride;benzene-1,2,3,4-tetracarboxylic dianhydride,thiophene-2,3,4,5-tetracarboxylic dianhydride, and combinations thereof.7. The aerogel of claim 6, wherein the polyamic amide polymer is acopolymer comprising the repeating structural units of:

where m and n are average number of repeat units per chain ranging from1 to 2000, and wherein X, Y and Z are the same as defined in claim
 6. 8.The aerogel of claim 7, wherein the copolymer is a branched copolymer.9. The aerogel of claim 6, wherein the repeating structural unit is:

wherein X and Y are the same as defined in claim
 1. 10. The aerogel ofclaim 1, further comprising a polyimide polymer.
 11. The aerogel ofclaim 10, wherein the polyimide polymer has a repeating structural unitof:

wherein X and Y are the same as defined in claim
 1. 12. A filmcomprising the aerogel of claim
 1. 13. An article of manufacturecomprising the aerogel of claim
 1. 14. The article of manufacture ofclaim 13, wherein the article of manufacture comprises circuitry, andwherein the aerogel is comprised in a substrate that is attached to thecircuitry.
 15. The article of manufacture of claim 14, wherein theaerogel provides thermal insulation to the circuitry.
 16. The article ofmanufacture of claim 13, wherein the article of manufacture is aradiofrequency antenna or a radome, and wherein the aerogel is comprisedin a substrate for the radiofrequency antenna or the radome.
 17. Thearticle of manufacture of claim 16, wherein the substrate is transparentto RF radiation.
 18. The article of manufacture of claim 13, wherein thearticle of manufacture comprises a face mask filter.
 19. The article ofmanufacture of claim 13, wherein the article of manufacture is aninsulating material for an oil or gas pipeline, an apparel, a building,or an automobile.
 20. The article of manufacture of claim 13, whereinthe article of manufacture is an insulating material for an aerospaceapplication.